Do you think one 212 is loud enuff for bar gigs? And if I have PA help do you think it will do fine?
Depends on the bar, the rest of the band's volume and whether you need the lowest notes to come out at high SPL. A 212 cabinet will not be as loud in the lowest range as an equally sensitive larger speaker, which means you'll need to change the tone settings. Whether you'll have an actual equalizer or just a bass control, it means that you'll either need to boost the bass or cut the mids/treble. In either case, you won't be able to play as loudly as if you already had the low end.
Think of it this way- if your amp is capable of a certain power output, that's without using the tone controls/boost/EQ. If you boost the bass, the demands on the amp change and this means your power at the distortion spec decreases because the power isn't unlimited. If you boost the bass and the speaker can't even produce those frequencies, it's a complete waste of power and you'll blow the speakers. However, you may be able to use the 212 cabinet with good results as long as you don't need super low notes or the speakers and cabinet are setup to handle them. This last point is rare- small speakers may do deep bass but they're not usually efficient in that range. This means you'll need to send more power to them in order to hear it as well as you need.
The first thing you need to do is determine the frequency range you need to use, then select the speakers based on this. Once this is done, you can select the amplifier- get the features and control you want and then buy the power. This is a good argument FOR using a separate preamp and power amp- you get the controls and features you want and if you really don't need a lot of power, you don't need to spend so much on that. Sure, it may take up a bit more space, but it gives you more control over what you get. For instance, if you need the controls and DI with XLR, like what a Gallien-Krueger 800RB has, the 400RB or 700RB won't quite do it. They'll work well, but power, bi-amping can't happen and control over the sound will be less.
You need to hear yourself when you play. If you don't have enough speakers or power, you won't. I wouldn't expect the monitors to provide this, so you may find that your rig needs to. The PA is for the audience, not the band. If it's a large system and has side-fills or large monitors that can be mixed to let you hear yourself well enough, great, but don't expect this to be the norm- just the exception. Some bass players like it loud onstage, some don't. You'll need to determine where you fit.
