Just a good 4 channel will do. Just test out the RMS is really sufficient, as it state in the technical spec or manual. 75w x 4ch will be good enough.

Another option is direct the component set from HU, and a 2ch amp for sub-woofer.

Ya Ya, start with 2 way. Really big head with 3 way. I'm using 3 way, still can't get a perfect position.

Choosing speaker and amp look for matching and like for a like.