locaps are the standard magazine size. They generally hold 60-70 BBs.
hicaps hold more, but you have to wind them up after a certain amount of rounds are fired. most you have to manually wind, but there are some electric winding ones. they can hold 200-500 usually, there are also drum mags which can hold more
midcaps are in between locap and hicap, they don't need to be wound up and usually hold 100-130 BBs
then there are realcaps, which hold the same amount of BBs are a real guns magazine would hold in bullets. so M4/M16 realcap would hold 30 BBs, while a G3 realcap would hold 20.
I also suggest the 416 as your primary. Maruzen and Marushins are nice, but I find them more collection pieces (just my personal opinion). For the field I would go with something a bit more reliable and cheaper like a TM P226, hicapa or KSC glock. there all great performers and there are lots of upgrades and accesories for them. WA makes really nice GBBs but they are much more expensive. Since these are your first airsoft guns I would stick with GBB for now, if you really like airsoft you'll probably get a good collection over time like many of us, so you can always look at AEPs later on.