I might sound harsh, but here we go.
I see lots of fancy and expensive things being consider, so no comment on that, but here's a differnt look at it on the cheaper side and still provide great stuff.
Consider the following (what I did 4 my 4 player, sf being the core)
4 happ competition stick - one of the best fighting stick, too. - about 8 to 10 bucks ea
1 happ super stick - good 4/8 way - use mainly for 4 way - yet another 8 to 10 bucks ea.
happ concave button - 1.5 or so each. True arcade feel to me.
trackball and spinner I will leave alone. stay with happ if you can...
encoder: conbination works here:
2 gpwiz max - 1 doesn't have enough input for 4 player . still need something for the trackball/spinner.
1 keywiz max + 1 gpmax - allow u to hide admin buttons and use shift key.
2 eco one - only if you want to mess with wiring... cheaper...
ipac mini - 1 ring solution, more expensive....
that's all for now...