It sounds like adding a second battery is almost required for all of that equipment along with another amp.
This will depend on how much anchor play time you want. Im a huge fan of a dual-bank system on a boat, regardless of stereo draw and anchor/sand bar time.

Hard to beat a simple 1/2/BOTH/OFF switch.

Can I get the revs powered now and add the additional components as funds allow?
Absolutely, because a pair of rev-10 are going to occupy all 4 chnls of an HTX-4. So adding bow speakers later, will not be hinged on your tower setup.