You should be able to carry a good sized room with just the amp and no mic. But if you gotta mic you can eq, I've heard others using bass kick mic's for bass amps. I use a standard mic and tune it in for the pa speakers and it really sounds great. I don't know about the need for a sub unless you do get a larger venue. But give your pa set a try. Back off on volume and set your eq if you get popping in your pa speakers though, don't wanna blow 'em.
If your mixer has a setting seperate from the gain so you can see when the channel clips that helps too, have your bassist play at volume and set it so the light comes on very seldom so you don't overdrive the channel, and then go to the gain to get your mix.