Three's plenty if you select them correctly: Loose, medium and tight. Actually you won't need the tight one unless you shoot handicap trap or a hunting environment requires it.
Of course, there are various degrees of each choke. My R-1100 trap model came with three screw-in, over bored chokes: full, extra full and super full. In .410-bore Skeet tubes, I have screw-in chokes who's difference is so subtle it's probably undetectable by the typical gun owner.