Just to verify what others have said, with a Form 1 you absolutely do have to engrave the gun with your name (or trust's name), city and state. You need to put it in a visible spot on gun. The exact verbiage escapes me, but it's something like "receiver, barrel or frame", though I recommend the frame because then you can use multiple uppers without engraving each one. There are minimum height and depth requirements as well.
I would actually recommend having a company build an upper for you. They'll build it and test it for function. Otherwise you might have to work at making it cycle reliable. Someone mentioned Noveske. Other options could be DPMS, CMMG, even POF or LWRC depending on how much you want to spend and how long you want to wait.
I went with a 7.5" AR and love it, but I might get an 11.5" "Commando" length A2 upper just for another option and the fact that I like the look.
Lots of us here don't mind answering questions about our Form 1 projects, so if you have something specific you want answered, just ask!