I gigged for ten years only owning one bass, then the internet came along.
I think it's not how many basses you need, more a question of how many tempting websites you don't need.
I could do the whole of our next gig with a J or a P, active or passive, long or short scale, hollow or solid body, etc etc, and nobody would know any different.
If I had to sell up nearly everything I'd keep a fretted and fretless as they'd do everything I need. Oh and my doublebass but I assume we're not counting that sort of thing.