Unless you are at an extremely short track, -1 +2 will be too low, I tried that at Pembrey and kept hitting the rev limiter.
I would say just go -1 on the front to start and then see how you like it or -1F +1R, which is where I am at.
As far as I know, neither the gearing or the tyre size will make a difference to the TC, I have tried 190 an 200 section rears and it made no difference, I also have changed the gearing and again it made no difference.
The factory builds in a 10% factor to take care of this.