AAA development just means you have a very huge, expensive team. Your question translates to "how small can a team be to still call it huge and expensive". The answer is simple and meaningless: Get as many as you can for as much as you can afford. That isn't strictly limited by your pockets, but rather by what you want to spend. How much you want to spend, on the other side, can depend on things like "how much are we going to sell?", which might be far less than your pockets are deep.
You might expect that in a AAA (senior) team, things will be more structured, but the opposite is the case (Just ask anyone here, they will "tell you stories"). Far more things will go wrong, far more things will happen than you can handle and resolve, but that's when the advantage of an AAA team will come into play. On average, you can expect things will turn out fine. If you hire 100 peps, you won't be able to avoid bad apples and Wallys, but the average dev will be someone who does his work and does it just fine, their efficiency might be 90%. On average, you will get some 80% game. On average you will get your money back. In bad cases, it will be an Anthem or Homefront 2 game. In good cases, you might get a Bioshock, Crysis or Gears.
The key is: 1. you hire many many devs. 2. you don't really care about keeping it minimal, cause you want to get enough to keep the average at average. 3. You might want to add some experienced leads to the pool, but you'd rather hire 3 random non-senior/non-junior guys than one really skilled.
IF you deviate from this idea, by trying to keep it minimal, you completely shift your risk. Imagine you have 10 guys and 2 don't get along at all. Your project might be busted. You might get them to cooperate, but then it might just blow up and it's insanely difficult to replace one key member of a team of 10. ( Yes, sure, you could expect professionals to be professional, but many in the industry are ego driven and chances are high you will end up with one of these in your team. )
Also: Don't expect that a new AAA team means you get an AAA game, it might be just AA. And eveb AAA games don't lead to AAA sales.
On the other side. Minecraft might be not even an A game.