Well you are almost equipped to do none of what you listed.
:lmao:
No kidding!
Riverlake, you need to do more reading!!
You spent way too much on an inferior body for sports and action, and unless it's 1:00 in the afternoon, a lens that won't let you do what you said you need to do.
Since you're willing to buy used gear, you could have bought (in the Nikon system) a D2h and 80-200 f/2.8D for as little as $1400. There's difference between 200 and 300mm, but it's not HUGE, and with the sharper images you'd be getting from the 80-200, you could crop down and still get better results than with the 70-300 on the d200.
You're not going to be able to use most of the AF sensors on the D200 anyway because they're not cross-types, and at 300mm you're at f/5.6 so if it's a night game, they might not even be able to pick up anything, and they'll be shaky becuase you wont' be able to freeze action anyway unless you use strobes or shoot at noon.
300mm at 1/125th f/5.6 ISO 1600 is a recipe for disaster in the sports arena. 200mm 1/500th f/2.8 ISO 1600, might be just as noisy, but it's at least feasible to freeze motion. To get to 1/500th at f/5.6, you'd need to have an ISO of 6400. Unless you've got a D3, YUCK, you're outta luck, the D2h looks like junk at ISO 6400.