One razor is fine, two is better. That way if one goes dull you still have another to shave with in the meantime, especially if you nick one it may take a few days to get it back into shape.

Straights are like puppies, though, they just tend to follow you home, which is why so many of us have multiple straights, especially once you get to where you can restore old vintage razors. Especially if you've got a little bit of disposable income, picking up one or two razors a month is still pretty cheap and once you get a few razors they just seem to multiply like rabbits.

As for time between honings, that will depend on a *lot* of variables. Some guys can go seveal months to a year between honings, some only a few weeks. Especially when you're starting out, don't be surprised if it's very short, this will lengthen as your technique improves. A pasted paddle really helps with this - like Ilija (firestart) I very rarely have to take a razor back to the hone, as the refreshes on the paddle seem to keep them ticking along just fine.