What are the recommendations for speakers? I assume high efficiency is the key. Can I run some high efficiency Pro audio monitors full range to room filling volumes?
The answer is probably yes. If your room is an airplane hangar, then no, but if your room is reasonable, then you should be just fine.
Can I power it with my Dewalt 18 volt rechargeable batteries?
That's kind of been a running joke in the office, that we should build an amp that will take a power tool battery. If you can figure out how to make good connections, that will work just fine.