Realistic answer:

If you don't need a suit every day for work: I'd recommend you still have one. Dark Navy Blue or Charcoal. For special occasions/interviews.

If you need one every day for work: I'd say you need a minimum of 3 to avoid looking like you don't change clothes. If you have a few different color dress shirts, 5, and 5 or so ties, you can make a Navy, Charcoal, and Light Gray suit look like a dozen different outfits. They should all be wool, because those are more considered all-season, vs a linen or cotton suit which is exclusively for warmer weather. I know people here may like to say "3! but I want to be as minimal as possible!"...any less, and really, your co-workers will comment. Wearing 1 suit over and over again is the equivalent of wearing the same T-shirt and jeans every day; it's obvious.

Unless you're in a position in life where you go to very high-end dinner parties and events at least twice a year, I wouldn't recommend buying a black tuxedo. There are very few parties and events that require them, even in NYC and LA; you're talking about formal balls, high-end art shows, and expensive Broadway plays. And most of the time, in those situations, you can get away with a navy suit and a black tie.