TS, if you like the D7000, just go for it! It's a pretty solid camera.
Don't worry bout people saying the colors being yellowish and washed out. I would describe it as warmer and flatter colors. My guess is that the peeps who say the colors are yellowish and washed out are probably Canon users.
Canon colors out of the camera seem more natural and tend to pop out better at least to my eyes. PP these days can easily correct the colors to your liking. I'd personally prefer Nikon colors for playing around in PP.
As for the af, I don't think the D7000 af will be much of an issue to an event shooter like you. Many Canon wedding/event photographers have made do with Canon's dated 9-point af for years.
I have successfully shot low light indoor sports (basketball) with a 60D which has only a 9 point af. It does miss 30% of the time. But probably 20% out of that is due to my own human errors.
I think the 39 point af is more than enough for shooting events despite its 9 crosstypes. If you are really concerned bout crosstypes, the 7D might please you with its all 19 crosstypes.
Seriously though, most people don't need so many af points, being them using only the center af. It's not impossible to shoot a whole event using just one af point. I've shot a church event using a Nikon D40 which has only 3 af points! No problem for me!
On the Sony part, well...I don't have much experience with Sony cameras except playing with the 10FPS one by shooting the 10 second countdown board thing in the store. What I do know is that Nikon and some other brands use Sony sensors, and they are excellent at high ISOs.
As for Pentax, I've never touched one before...as they are not so common and readily available as the typical C, N and S brand, so yes, finding compatible equipment will not be as easy as the other typical camera brands.
Therefore, just buy what you like, but take note of the disadvantages of each brand and work around it. Perhaps a D5100 is good enough for you since you have a budget? Or maybe a nice FF with amazing high ISO if budget allows? I can't really answer that for you. There is no perfect camera for everyone. To each his own. Try as many models as you can. Buy the one you like.