just my 2 cents.
A small head goes a long way and is extremely flexible. For instance i have a fender rumble 150 head. it puts out 150 watts at 4 ohms. it is a very inexpensive head at only about 225 brand new and maybe less than that if you wait around for a coupon or know someone at the music store. there are others like the hartke 2500 comes to mind right off the bat. Some people would say that 150 watts wont get you very far with a band but it really depends on what speakers you pair it with. I have 4 different cabinets that i use depending on the application. A markbass 6x10, and fender 4x10, an old peavey 1x15 and a very old Sunn cab loaded with a JBL E140.
the markbass is by far the loudest because of the sensitivity rating at 104 db and 6 drivers. this head and cab is easily as loud as many 300-400 watt amps paired with an average 4x10 which usually have spls around 96db. for a similar tone but less of it I use my fender 4x10 which i would guess is in that range of around 95-96 db but i can't seem to find any specs on this.
for an entirely different tone i use the old sunn cab. that JBL E140 is an absolute monster for tone. and with the JBL's fairly high sensitivity rating of 100db it is still very loud, even with only 150 watts pushing it.
i usually just keep the old peavey at home. i traded an old cheapo distortion pedal for it and it does fine for practicing at home. if i did not have the other cabs i would not be afraid to take it to rehearsal or even a small gig but my others sound so much better.
you can find a good small head used pretty cheaply on CL or "the bay" as many people are into having huge wattage to get more volume and never realize that just getting a more efficient cab or adding another identical cab will add more volume to the their sound than doubling their wattage.
i also have a fender 2x10 350 watt combo. the 150 watt head and 4x10 is easily louder, lighter than the 2x10 combo.
Lastly, a head and cab is more flexible because you can change one half of your tone combo at any time while keeping the other. you have the flexibilty to swap heads around and keep the same cab.
welcome to the wonderful world of bass. i hope you love it here as much as i do and good luck on your quest for tone.