If you are only coating parts, then you do not need an FFL. If you plan on doing serial numbered receivers or frames, then you need an FFL to accept custody of the firearm.
No, that should be fine. You need to check with your state laws. Sometimes the person "borrowing" the firearm may need to have an FID or Handgun Permit.Are y'all saying that, legally speaking, if my buddy and I go out shooting, and for some odd reason or other I say "I'll take your rifle home and clean it up for you", I need an FFL? Wow....