On a regular non-beadlock type wheel I always use a general rule of a tire that's at least 2" but not more than 4" wider than the wheel.
But with a beadlock, as mentioned it can pretty much be anything you want because the bead is physically clamped. So you could theoretically run a 9" wide tire on that 9" wide wheel.
But then they start to look a little funky with the sidewall pooched out some.
The good news is that most, if not all of the tires you will be looking at have a recommended rim width associated with them. The important bit about that fact is that the larger tire companies, and probably a lot of the smaller ones now too, will only mount a tire to a wheel that fits within that range the manufacturer specifies.
I tend to go narrower slightly than the tire manufacturers normally do, with maybe a 12.50" tire on an 8" wheel instead of the usual 8.5 to 10. But the larger chain stores won't do it anymore.
Paul