| That's a pretty good setup to get started with. If your band isn't too loud, it should work well. From my own experience the SVT-450 isnt as powerful as its power rating would suggest. The 210 cab can handle a good amount of volume and can be considered loud in a small bar/small jamspace context, but I wouldn't recommend going into extreme volumes with it, at least not if its used as a standalone. I own that cab too and so far I've used it as a standalone, but I usually play smaller places, so I haven't had any issues with output unless the place sounds bad to begin with or if I'm playing with a drummer that's real loud or has a really loud drumkit.
You should be good with that setup, but if you ever need more power, I'd start by switching out the head before adding a second cab. You can get used, older GK heads like the 400RB or 800RB for good prices and, even though the listed power rating may not be as high as the SVT-450, I can tell you from firsthand experience that they will outperform the SVT-450 and not overload the cab since it handles 200 watts. | 
