Err no...you dont have to be registered to sell it. You just have to be certain that the person you are selling to has a legally valid reason to purchase the RIF from you.
Although you said that the re-enactment group is expensive to get into, that may be your only option if you don't want to go the airsoft route. If you were to become an official re-enactor you may be able to get exemption to allow you to posess the an RIF. However, I don't know the exact process...
I agree with devastator about using your first gun before getting a new one. You should go to the skirmish you mentioned and first see if you actually enjoy it and if the site is a good one.
Perhaps rather than taping it you could use a gun wrap or scrim netting. Would be easier to put on and take off at the site and would probably look better.
Personally i think camo tape looks terrible.