RE: You can have 3 calibers, nothing else...
Only 3 -- harkens back to when I was 16, nowadays I would choose:
Including shotguns: 22LR, 338 Win Mag, 12 gauge.
Excluding shotguns: 22LR, 7mm Rem. Mag, 338 Win Mag.
Excluding shotguns & 22' s: 22-250, 7mm Rem. Mag, 338 Win Mag.
If you only have a few, keep them spread out -- no sense in clustering a group of essentially equivalent cartridges.
Never Go Undergunned
EKM