I suspect your weakest link is the bass end. With low frequencies being undirectional a microphone turned up loud enough to be heard will also be very susceptible to feedback.
With that in mind I'd suggest putting a pickup on the bass Bally. If you're sure you're not playing in hostile environments then mics on the others might be ok. Personally I'd be looking for pickups for them too.
Alto active speakers got a good review in SOS. I bought a pair of 12"s for 400 quid and am very happy with them.
There are a few small mixers to consider. Have a read through the "live sound" forum to get some background info.
Ohm's Law states, "Your PA isn't as powerful as you think it is".