You can bowl with just two balls and a spare ball and do fairly well. However, that really limits your options and forces you into a corner if they're too dry for your only solid and too over/under for your only pearl, and your carry sucks playing the line it forces. I tried for years to only carry two balls, and I finally realized that it was really limiting my options when I saw different lane conditions than the norm. My accuracy, consistency, and often carry suffer if I make more than small to medium changes in my release. It's not for lack of practice and coaching, I'm just plain not good at it no matter what I do. I have my A and B game releases down pat, but my C and D game releases are just horrific.
If you bowl in more than one house, you really should give yourself options as you will see a variety of lane conditions and oil patterns. Two solids and a pearl, or one solid and two pearls (or two of each if you aren't good at changing your release drastically, like me) should give you the chance to play different parts of the lane with different angles and still carry well.
Most people on this site use too many bowling balls. There are the opposites like cool rockin daddy who feel you should be able to make any ball work on any condition if you're talented enough (physics dictates that this is just not true). The best solution is almost always in the middle.
