I'd also recommend a matching cab (assuming they are both eight ohm cabs) strictly because the load is well shared between the two of them - both links in your tonal chain are equally strong so you won't blow up the weaker of the two. If you stack them so the speakers are in a vertical line you'll get more sound up toward your ears at the very least.
It's conventional wisdom (and I share it) that 400 watts and a 4x10 is enough for most situations. That assumes that the drummer and guitarist(s) aren't complete maniacs. There are a lot of nay-sayers to that, I'm sure. In my experience it's true.
As said above there's nothing wrong with going through the PA assuming that the PA is good. DI is preferred if you aren't depending on effects for your tone. Your cabs add color and the mics add color. I usually just want a clean tone to get out to the PA. If your amplification/effects are integral to your tone a mic is preferred. A good mic for bass will get you into the realm of a second cab, price-wise.
I think a matching cab will get you where you want to be. The head has a DI and that should be enough to get you heard out front.
Good luck.
KO
+1
It all depends on the PA and the stage volume of your band.
Is the PA designed to deliver bass to the audience (as opposed to only vocals and maybe keys)?
- yes: just use the DI on your amp to get your sound to the PA, and use your cabinet as a stage monitor for you to hear yourself. Don't count on the PA monitors, bass usually sounds terrible through them and volume is often a problem.
- no: avoid going through the PA by getting an extra (matching) cabinet so you are sure to be able to fill the room with your own equipment. For bars and small clubs, this shouldn't be a problem with your setup + another 210
Does your setup have enough volume to get your bass to sit nicely in the stage sound mix?
- yes: no need to get an extra cabinet, as long as you can go through a decent PA.
- no: get an extra cabinet and some ear protection.
I use a 500 watt marbass head and a 410 cab, and I have no problem hearing myself on stage in a loud band with the master at 9h00. Also no problem at all filling a 300 people sized venue with good tone, while keeping ample headroom, when I open it up a bit further.