I'd certainly be looking at the hosting issues, as you have some cracking kit, which would offer good options at Donington.
It doesn't look like the weather did you any favours, but you've found some decent angles free of the catch fencing.
The shots all look like you've been fairly brave with the shutter, which has brought about some good wheel blur, but the softness of the images detracts from this. There are some elements of sharpness, but I wonder whether your autofocus settings were optimal for what you were shooting.
I'd be looking to use AI-Servo for these type of shots, and track the car for a short while before shooting. Aim to get focus on a critical part of the car: front grill or helmet if shooting from the front, or the number if shooting from the side.
It's best to start at a higher shutter speed to start, to ensure that you are getting the sharpness of the image that you want, then reducing down to get the level of blur you desire.
Also, whilst frame filling car shots do have a place, I think its nice to factor in the surroundings, by shooting a little wider. Donington isnt the most scenic of circuits, but there is definitely potential there to make some very pleasing shots.
And yes, a little contrast and clarity can help motorsport shots in PP, so it can be beneficial to have a tinker, once you are confident that you are getting the most out of your camera first of all