The Culpepper-Fredericksburg area is amazing for Civil War trekking because all of the fields are so close.
I did a swing a couple of years ago where I visited Rappahannock Station, Brandy Station, Kelly's Ford, Cedar Mountain, Payne's Farm, The Wilderness, and Chancellorsville all in one day. (I did much of it on foot - I'm a fast walker.)
Depending on the tempo at which you want to move, I'd recommend 1.5 - 2 days for the Fredericksburg area fields.
The Wilderness is heavily wooded, and there aren't that many trails, so it's a relatively quick visit.
The Sunken Road area of Fredericksburg isn't that big - be sure to visit further down the line as well. (The hike up to Lee's observation point is STEEP.) (The American Battle Field Trust's breakthrough trail is okay - only worth it if you're familiar with that element of the battle.)
The Chancellorsville park is really structured around Jackson's flanking march and the site of his wounding, but be sure to visit Hazel Grove, where very heavy fighting took place on May 3. (The May 1 trail, which is owned by the American Battlefield Trust, isn't really worth it.)
Spotsylvania is amazing, but bring a compass. Every time I've been there, I forget which way is north. (The Harris Farm marker a couple of miles east is interesting, if only because because you're probably trespassing to get to it.)
Stay the night in Fredericksburg if it's in your budget - it's a neat town.
Manassas is a full day.
First Bull Run isn't that big, but the complexity of Second Bull Run requires a few hours.
Depending on traffic, Antietam is two hours maximum from Manassas (Take US 15, not the Beltway to 270!)
If you're coming up from Georgia, Appomattox seems best for on the way back. (You can sort of get to it from US 15). I'd recommend starting at Five Forks and following the Lee's Retreat signage / guide. It's about 100 miles and covers all of the key points on the road between the two.