New Basement Setup

I'm finishing my basement and decided last minute on some in-wall speakers mostly for TV/movies, but also added a few extra basement speakers and external for music. I jumped in quickly during construction before thinking through the system. Here is where I'm at:

Center: 255c-RT
Fronts: 265-RT
Rears: 700 LS ( I only have space with layout for 2 surround.)

Also in basement, x4 620-RT to extend music throughout space.
External: Atrium 5 x2

1) For the rear I could do 700 LS or 620-RT, which would you make surround verse music in rest of open area?
2) Recommendation on AVR to support setup?
3) I need to get a sub too, recommendations?

Any advice appreciated, TIA.