Compund wise, talk to your Michelin trackside rep. Sure, you can mix compounds. But they can look at your current wear and make a better recommendation. Also, keep in mind with the hotter summer temps, a Soft rear might not last too long.
Also, you might wanna look at the Power One's. Fantastic tires!
From what I have heard, it is usually best to have a softer front than back as opposed to a softer back than front. If the front end still sticks with the med front then go for it, but you don't want to have the front end washing out.
70 series will offer better stability, also most do not run harder tire in the front with a soft rear.
Remember we are not riding in MotoGP.
Seeing that you are asking everyone, you may not have a lot of experience with track days, if so ask someone who knows your track and bike, well. Or just be safe and run a set of softs, front and rear.....Scrub them in at the recommended pressure (track pressure) reset pressures after your first session and just have fun and get to know your bike in a different way.