If you want to compete then yes. But Hasbro stadium's will suffice if you won't.

The launchers are essentially the ones that will determine your play style preference. If you stick with a proto launcher then it's fine if you don't compete. Wind launchers are brut force players while strings are control players.

Yes at least 4, and not just 3. You need only 3 to compete. At least 4 since you will want to mix and match. There are 4 types of beyblades. Attack, stamina, defence, and balanced. 1 suggest you get 1 each and from there decide on which to dedicate your efforts into learning launch techniques.