>>303757804 boxes reserved to hold whatever I need to breed what's in my trading list
5 boxes of breedjects / GTS fodder ordered in decreasing order of value
I prevent having more than 5 boxes of breedjects by releasing the worst breedjects of each type, wondertrading is too slow.
1 box of essentials (current team + utility mons)
1 box of showcase (pretty mons, legends). Optional, 1 or 2 boxes of special showcases (like minior forms, vivillon forms, that sort of thing)
1 box for eggs (I try to keep this empty)
Any remaining boxes are random mons I've caught for dex, I usually separate FE from NFE.