To my knowledge there is no magic number, i've seen pics of member gun rooms here that looked like a friggin gun store. So you can have as many restricted as you want .
They may ask for a safety check to see if security wise you're ok but there's no definite amount/number of restricted that you're allowed to own
Edit: i mean if for any reasons you raise red flags (neighbors are worried, seen you waving guns in the window stuff like that) you will be bothered but if you're enjoying your sport/hobby within the law i dont see why they would spot check you every so often once maybe after your XX purchase see how you're doing