I just last week submitted my first form 1 for an sbr. Really easy actually with e-file.

I would get the upper and lower first, then get your fingerprint cards (I got a 25 pack and a dry ink pad thing for about $10-$15 on Amazon, and youll definitely want extras because you will screw up, at least I did), then file the form and send the cards in. The form asks for barrel length and overall length of the complete firearm, plus markings on the lower. Then just "assemble" once its approved.

Engrave after if you are, though Ive seen where people have directly asked ATF about engraving, and were told they had to engrave the "maker" info if they intend to sell it, much like 80%s are/were handled. So Im on the fence about if Ill even engrave mine, Ill look into it more when I get approval.