A:
This really depends on how loud you want your music to be. My first thought is to use a 1,000 watt amplifier and run higher power line transformers such as Lowell TLM10070A High Performance 100W, 70V. You can go down to lower taps such as 32 watts or lower like 10 but 10 would be really just for doctor's office type background music.
There are more receivers now-a-days that can distribute power to multiple zones as well. But do be careful as most of the multiple zone receivers will still require you to have a separate amp. Most of the multi-zone receivers are only giving you extra "pre-amp" outputs which are no more than RCA output jacks to connect to another amp or receiver...