i play bass, although not really professionally. i'd say jump on some bass forums, they do exist and you'll find heaps of knowledge on there. i've got a 15" combo although i find it way too boomy. i'd say go for a 4x10" quad, you'll get a bit more definition. look into ampeg heads, mate has one and it's pretty nice. advantage of going for that size quad is you can also get a 15" later on and use that aswell.
another thing is to just go around to music shops and try out what they've got and see what they have to say.