It's about three years now since I bought my first bass, and before I splashed out the money, I asked a few questions around here. Such as, "will I be able to play my bass through my guitar amp?" to which the unequivocal answer was, "NO! Get a bass amp."
So with that in mind, I tried a few amps in the shop where I bought my bass. The one that caught my ear was the Roland Cube30W bass amp - tried the bass I was buying through it, and it sounded fine to me. I already had a Cube15W guitar amp, and liked that, so it didn't take too much persuading to sell me on the bass amp.
After a few months or so, I decided that, just for a change, I'd take my bass up to the acoustic jam in the local pub. I don't think the volume got much above about #2! Since then, I've used it at jam sessions when others have had electric guitars plugged in - even then I never got much above #3.
So for home and small pubs, I'd say a 30W bass amp would do you fine - maybe a 60W if it's a largish pub. I did try the amp once at higher volumes, to see how loud it could get - anything above #4 at home, and those windows were rattling! I didn't dare push it any higher.
"Sometimes the beauty of music can help us all find strength to deal with all the curves life can throw us." (D. Hodge.)