ATF’s own Q&A will tell you they can still consider you a dealer even if you are losing money.
To the OP, the state of NC has nothing to do with this question, other than the very rare instance where they go after you for sales tax, in which case it would be because the feds have already gone after you for being a dealer.
There is no magic number in statute that defines someone as being a dealer and needing and FFL. If ATF decides for one reason or another to go after you, you have a 99% chance you’ll find out because they will pay you a visit first and have a friendly chat about needing an FFL.
I wouldn’t sweat it, if I were you. What I’ve seen of your selling on the forum is a drop in the bucket compared to what a lot of other people do on forums and at shows. And, selling stuff you have to upgrade your collection is something they specifically address in their Q&A as not making you a dealer.