Check tirerack, they have the recommended tire width for all sizes of wheels. I'm not sure what to say for 9" wheels though.
Do you really want to go that wide? I would actually say that's too wide.
Wider can be better (for certain types of conditions), up to a point. Consider that contact patch will be roughly the same as that of a tire on an appropriately thinner wheel, but it will just a different shape (shorter and wider versus longer and narrower). I don't think I'd ever go wider than 8 or 8.5" on these cars (there is no point), and if I did I would go for one of the thinner tires that I could fit on the wheel (unless you like rolling fenders or have an STI).
I have 8" wide wheels in a +48 offset and if they barely tuck into the wheel wells when the suspension is compressed.
But back to the question, if you insist on going with a 9" wide wheel then you will probably need at least a 245 width tire. 255/40/17 would be ideal, but it just depends on how much you want your speedo to be off by. In that size your speedo will read 0.168% faster than with the stock wheels. Keep in mind that the speedo, with the stock wheels, already reads a little fast, probably by ~1mph or so.
What is your goal as far as tires and wheels go? I would suggest picking a few potential tire sizes first, and then finding a wheel that will work with one of those sizes.