How much do the risks increase if I'm diabetic and having uterine cancer surgery?

Depends on control. For the most part, if your diabetes is under good control and you are on a stable medication regimen it shouldn't change your risk much. If you are very Insulin dependent, managing your Insulin dose while you heal and regain your appetite can be a bit tricky but still very easily accomplished. Your risk shouldn't meaningfully increase unless your control is very poor or you have heart disease.
Depends. Diabetes is a risk factor for post-operative complications, especially infections. This is especially true if your diabetes is not well controlled.