Re: mixing cabs and heads
Hunt around for a used 2x12 cab and 50 or 100 watt tube head. If your patient and a bargin hunter you'll come up with something totally usable for $600-800. I found my Rivera 2x12 used for about $275 and you can usually find Sovtek or Carvin heads, maybe even a Silverface Fender Bassman for $300 or less...even a Marshall Mosfet with some stompboxes would be 'better' then a Line 6, Crate, crappy solid state Marshall or some Ivebeenhad piece of poo. At the very least you won't want to sell it in a year. And I'd go with a 2x12 cab over a 4x12 unless you have a big car and a roadie to carry all your gear all the time.
Go to the stores and try every used amp you can find. If you like the clean on one or it only has a clean sound then get a kick-ass stompbox for dirt, call it a day and go make some good music.