This is pretty long, but hopefully it will explain some of the "stuff" that is frustrating you.
Some people want to be historically accurate in every detail. Frankly, I'm one of those, because I really love the "time machine" aspect of reenacting and want to be living in the Civil War period 24 hours a day, and I understand and respect others' wanting to do the same. However, for various reasons, I do have to compromise in some areas, which I'll detail. While some "mainstream" reenacting organizations stick with the "ten foot rule," I feel that I have to be more accurate than that, because most of my interactions, both with the public and with my living history colleagues, involve being a lot closer than that--usually sitting or standing next to them. However, I would not tolerate anyone's checking out my underwear! I also refuse to be a "stitch nazi," the term often used by "mainstream" reenactors to describe the "progressive" (more historically accurate) group. I personally strive towards the "progressive, but I keep my thoughts to myself unless asked.
Your experience does show, as an example for others, that when joining a group, you need to find out their standards up front before making any purchases, and to ask for their guidance on everything up front. It might be that you would be more comfortable with a more "mainstream" group, which may list the same standards but is less intent on enforcing every detail. However, the closer you can come to accuracy up front, the less you'll have to spend to correct mistakes later! I suspect that this may be at least part of what concerns the folks who are trying to mentor you.
Footwear would seem to be hidden, but actually it is going to show--and be observed--every time you lift your skirts to navigate stairs, curbs, and other obstacles. I have medical reasons (severely deformed feet requiring basically prescription shoes and insoles) that prevent me from wearing reproduction Civil War era footwear. About the best I can do is to wear black leather laced oxfords (highly supportive New Balance walking shoes with the markings blacked out with lots of shoe polish) with black stockings (so they blend in) and try as hard as I can to keep my feet hidden under my skirt (those thick rubber soles are a giveaway). If you don't have my medical problem (which fortunately is a valid exception), there are modern equivalents (such as cheap jodhpur boots or similar) that can be used (you'll need to avoid or disguise any zippers). Flats or Mary Janes (preferably with thin leather soles) are an option, although not too practical for outdoor events.
One caution on underwear: With the snugly fitted bodices of Civil War dresses, it
will be quite apparent to all but the most ignorant if you are wearing a bra (not in general use until after World War I) instead of a corset.
You definitely need to come as close as you can to that smooth line from bust to waist (more difficult for the stouter among us, like me, who need more engineering). If you're one of the lucky skinny types, you may get away with being corsetless, if you can achieve the proper effect with your bra (support from the underside only, and not raised too high). However, you can make your own corset, using cording instead of metal stays if, like me, you don't want the restriction of the latter. Elizabeth Stewart Clark's
Dressmaker's Guide has easy-to-follow directions. Nobody's going to look at it (at least, they'd better not!) to be sure you used period construction or those lovely impossibly tiny stitches. If you have to buy, check out Originals by Kay--at least hers will fit comfortably, unlike the generic corsets (aka instruments of torture) sold by sutlers. It is a good idea to wear something under the corset that you can change daily, to protect the corset from your sweat and you from the corset, but if you don't want to sew or buy chemises to start, a white cotton T shirt (as long as it doesn't show!) will work just as well. (BTW, another of the compromises I make is to use 21st century deodorant!)
Sewing machines were in general use in all but the poorest families by the Civil War, so no problem with machine stitching unless you're reenacting an earlier period (like 1840s). However, home machines in that era did not have zigzag stitching or machine buttonholers--straight stitch only. If your hand buttonholes are not up to snuff (mine still aren't, although I am getting better), use hooks and eyes (actually far better because you can space them close together where the closure is stressed and farther apart in other places), and, if you really want buttons, sew them on top (evenly spaced) as a decoration. This was a frequent period practice, as I learned from a workshop featuring lots of original dresses! Top-stitching was generally done by hand, but you can avoid most of that. If your thread blends in well with your fabric, machine top-stitching probably won't show (test it first!). In fact, using dark blue thread with my dark indigo blue dress (fabric shown below), I had considerable trouble finding my stitches when (as too often happened) I needed to remove them!
Some sewing techniques (especially the various methods of gathering) are actually easier, faster, and more effective using the period hand techniques. I was amazed!
Depending on the occasion, you at least should have sufficient petticoats to make your skirt look appropriately full for the period (it needs to poof out, not hang down limply). The standard for the CW period is an under-petticoat (for modesty and to prevent the hoop skirt from getting dirty), a cage or hoop skirt, and a full over-petticoat (or maybe two) to hide the marks of the hoops showing under your dress. Except for ball gowns, 90" to 100" hoops are sufficient. If you are camping and working around an open fire, the cage or hoops should be omitted for safety (the drop-and-roll technique if your skirt catches fire won't work with hoops!). Even if you have no sewing skills, petticoats are easy to make (nobody will see your--or my--crooked stitching!), don't need a pattern (just rip straight panels of cotton fabric), and are a great way to learn to sew, saving lots of money. Again, instructions are in Liz Clark's
Dressmaker's Guide. Better yet, they're available for free on her website,
http://www.thesewingacademy.com, in the ''Compendium" section (which has lots of other great articles for us reenactors). Drawers are optional, although advisable if you're young, active, and wearing hoops. As an old lady (81), I would be of the generation that still considered drawers downright improper if not sinful (they are, horrors, a male garment)! For all these underpinnings, the quality of fabric needed depends on how often you'll be wearing and laundering them. If only a few times a year, white (not unbleached) cotton muslin is fine, and cheap. If you're reenacting often (such as weekly at a museum), where durability becomes important, cotton "Pimatex" is the closest we have to mid-19th century longcloth, and will last for years--but is far more expensive.
Once you've made your petticoats, you'll find that dress skirts (of identical construction, made of straight panels) are also easy--so if your sewing skills are poor, you can save money by having your dressmaker do the bodice (more complicated) while you make the skirt.
Finally, do avoid synthetic fabrics and blends, which not only are not period-correct, but. more practically, are far more uncomfortable when it's hot!
The biggest problem for me has been period-correct print fabrics for the dress, for which you'll need help from the experts in your group, or from Liz Clark's Sewing Academy Forum. While I'm not an expert, here's the fabric of my current dress--note the geometric aspect and the relatively widely spaced figures:
You can see what I meant about my dark blue thread's being invisible here! I was lucky to find this fabric at a mail-order discount store which carried discontinued fabrics.
I also have to compromise on my hair, since I normally wear it in a pixie cut and have decided that it's not worth growing it out and putting up with long hair (which I detest) for a half dozen occasions per year. So I use period-correct headwear which covers most of my hair and lots of hair care products to achieve the combing back,
de rigeur center part, and no ends visible for the front two inches of my hair that does show.
As I strive to achieve the "look" of the Civil War period, my "bible" (in addition to Liz Clark's book) is Juanita Leisch'
Who Wore What: Women's Wear 1861-1865. Her research was based on examination of thousands of photographs (CDVs) of that period. It provides a wonderful insight into the overall "look" you should try to achieve, and, since illustrated with all Civil War era photos, will give you some basis for coping with the "stitch nazi" types. Research is vitally important, but this lady has done a lot of it for you!
I did find out, though, that as long as I appeared outwardly "in period" at a normal distance (say 2-3 feet), nobody said anything or even checked anything at actual events, even events that were supposedly more "progressive" and had what sounded like really strict rules. I was, in fact, shocked at some of the deviations I saw! So do the best you can in outward appearance, trying as best you can to achieve the overall "look," and work on the more finicky (but hidden) details later.