99,999. At 100,000 restricted (especially handguns), many Liberal brains suddenly explode, and the powers that be are very worried about those tiny, tiny Liberal brains.
Seriously, I know folks with hundreds of restricteds, and a couple with several hundred prohibiteds, and they haven't had any issues due to the number. Rather, they have the same hassle that anyone with an RPAL has. Remember that duck hunters with double barrel shotguns are supposedly ok (for now), but nobody NEEDS to own a pistol or an "assault weapon." Plus, it is terrible how those nasty assault weapons sneak out of safes at night and go on baby-killing rampages all over town.
So, if you have an RPAL, you can "own" as many restricted firearms as you want, until Justine and the Queen's Cowboys change something and require you to turn them in for destruction.