So given it is a small section what type of concrete do you suggest I put there? I.e. Quickcrete, etc
Yep. Just plain Jane concrete in a bag from your local home store. If you give it enough depth and don't mix it with too much water, it will hold up like any other concrete.
Also, what do you mean by keyway?
Are you saying to make the top cut narrower than the base?
The picture above shows one of the joint's pinned and keyed. You also don't need to get this dramatic with it - just enough profile so the old and new interlock together. (Just roughing up the surface to expose the angular stone within the old concrete should be enough to lock the two together.)
The other thing I should point out is this spot is exactly where the front tire of my SUV is parked. Do you think with Minnesota weather and salt, etc it just eventually gave out in this area?
I'll bet that spot has some stories to tell..
If you had a salt or other chemical problem, then it would be in other parts of the floor. I'll bet that parking the car on top of a thin patch is what did it in. Thin patches don't hold up well under use.
That hole in the slab doesn't go all the way down to the gravel base currently, right? (If it does, you'll want to check for buried cash, time capsules, body parts, etc. before filling in.)