2. Where should I start? - Any suggestions on training and things I should know (ANYTHING helps!)
When my gym told me that I first needed to attend boxing, then kickboxing, then ground fighting I didn't understand. Ground fighting was what I wanted to learn. Now just 3 short weeks lately I completely understand why. Take it easy on your knee let your trainer know about your knee issue.
But you should start out with boxing which doesn't put to much pressure on the knees.