If you wait for the next round of sales, you could get a Sony A7 II for under $1k and have some cash left over for a nice lens. Full disclosure: that’s what I did
If you go with Sony/Nikon/Canon, it’s better start with FF. The reason is that a FF lens can be used on a crop-sensor camera, but it doesn’t work as well when you go the other direction.
I’ve used Sony, Pentax, Olympus, Nikon... they are all good! Tough to go wrong with any of them; just remember that you’re buying into a system as much as a single camera. And it’s expensive to change systems...