I have been guilty of a "just in case" arsenal. I used to bring five balls to league. Partly because I always took the same two bags with me whenever I step into a bowling center.
But now I have 2 balls for league. In fact, I am bowling in a sport shot league and I am taking the same 2 balls. Score the best I can with those two and then go home.
If I were a professional bowler, I would probably have more.
If I were a top junior bowler with aspirations to win Junior Gold, then I would take more. If I am going for experience, then those listed would be fine. The deal with Junior Gold, for those with a chance to win, is you will run across bowlers of more varied ability than a pro stop. All types of styles and all types of balls. Plus, many may approach the shot in a way detrimental to the top bowlers making transitions even more unpredictable.