right now I think we can say you need a stash of 250 FKG at all times, in case

I was lucky I could make 90 gems from the gifts and girls I have so I scrapped in this event

Realsitically this wont happen again but I'd say having 250 minimum spare and only spending if you REALLY want the spotlight girls (I blew 150 on Xmas and year years gachs can't grumble) or you have 300 at the time and figure, why not