KevyKev

Hello all, first post here so forgive me if I posted this in the wrong forum. Recently I've decided to do my first build and wanted an AR pistol. I found a good deal on an upper from Diamondback and received it last week. This week I ordered a stripped lower and having it shipped to local FFL. I'll be completing this over the next few months as its easier to sneak parts in here and there without the boss lady becoming suspicious of all the packages lol. Anyway so what exactly do I need to know on having this registered? Is there a certain way the dealer needs to do the paperwork on it as far as classification? Next question is on buffer and brace. Can I use a standard buffer or does it have to be a pistol specific buffer? I know I can't use a standard stock on it so any recommendations on a good brace would be appreciated. I've got some drop in triggers on the radar as well as charging handle, safety selector and all that. Just gotta decide on what I'm going with on those. Any help you guys can give me as make this venture would be awesome and I would be forever grateful. Thanks in advance!