The form 1 is for building, the form 4 is for buying. Since you want to form 1 as an individual, you need the form a set of ATF fingerprint cards and the form 5330.20 citizenship form, fill it out with photos and take to your CLEO he signs it sent to BATF with your check for $200 and wait for 3-4 months then they will send back a copy to you approved and you can start to build 1 silencer at that time.
This one time build it form is not for prototyping and future design changes or repairs, you are not a manuf. or licensed to replace any parts once you build it.
If you go the corporation route then there are no fingerprints, or photos or cleo permission but it remains an asset of the corporation and it transfers with the corporation or dissolves with the corporation.
Sof if you build a silencer you do it on a form 1 when you sell it most likely it will go form 4.