RE: how much wind is generally too much?
I think 15 mph is a good number...you'd better get used to flying in some wind as if you don't you're gonna miss out on a lot of great days.
Like combatpig said..if it's no longer fun then it's too windy.
I have flown my beaters in 30 mph + winds where I've had to land at 1/2 or 2/3 throttle. This is fun, but then again if I stuff my beater I don't really care...
More valuable planes are reserved for less windy days.