There's a museum of sorts in Falmouth, Virginia that has cases filled with these kinds of objects, all dug from the surrounding battlefields. The shame of it is that none of the excavations were properly documented so the collection is almost entirely uncurated.
But the objects are interesting in a lot of ways, including in the variation among common items like your "cartridge box belt plate." Some are rounded, some are almost flat, and the stamps differ in quality. They really illustrate the idea that mass production does not necessarily mean industrialization, and mass manufacturing does not ensure absolute uniformity.
But I'm not entirely sure how, with all those small variations, one could really tell an original "relic" from a later reproduction that had been artfully aged with an intent to deceive. If you're a complete novice as you say, perhaps it's better to hang around a little with more experienced collectors before committing. I think that would certainly be wiser than asking strangers on an internet forum.
It also seems to me that if they were all worth a couple of hundred dollars the White Oak Museum would sell theirs off rather than try to support themselves on a trickle of visitors at $1 to $4 a head. If you get a chance to visit, here are the directions:
https://www.visitfred.com/listings/things-to-do/museums-historical/white-oak-civil-war-museum I really recommend a trip for anyone who can get there.
Anyway, I count as a complete novice on these things myself. Good luck to you.
Bringing the