The answers...
To install a froward vertical grip on a handgun, you need to file a "
Form 1" to register a Title II "Any Other Weapon" you are making. You send the form, finger prints, CLEO signature, and $200 to the ATF and wait until they return it to you, approved with a canceled tax stamp, before you install that grip.
A silencer requires its own form, fee, and tax stamp. Unless you're making your own, that would transfer on a "
Form 4."
If you want to put a stock on it, you'd be making a "Short Barreled Rifle." You'd need to file a Form 1 to do that. But if you did that, the AOW issues wouldn't come into play -- it would be a rifle, not a handgun so you can install a vertical grip without a problem.
To sum up -- if you think you might want to put a stock on it, register it as a SBR. That will let you do the stock and/or the vertical grip. A detachable suppressor/silencer will be a separate registration, form, and fee.
There aren't really any good practical reasons to install a vertical grip on a convectional handgun as such would make your pistol almost impossible to holster and a forward support hand stance is not as fast or inherently accurate as the more traditional Isosceles (or Weaver) stances. But, if you just want it for looks or to try it out, it might be worth $200 to you.