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Green Day have three, as did Nirvana (After Jason Everman and Chad Channing left, Dave Grohl replacing Chad on drums).
We have 4, but also have a saxamaphone player and string quartet that sort of orbit us, but only Fat Joe (sax) plays onstage with us for a song.
Drums, Bass, Vocals/rythmn guitar, Vocals/lead guitar/piano.
Sorted
4 gives a bit more depth, but plenty of 3-piece bands kick the crap out of bands with more in terms of quality.
3 is fine.
Don't think you really need more than 4 maximum.