Great Engine!
Friction: 1.5 - 2. I thought anything less than 1 made the game too "icey".
Max left/right: -4/4. This allowed the character to barely make some jumps, but have some extra room for error on others.
Gravity: .8. The default .9 was alright, but it could use a little more floaty-ness to it. Letting the player move the character mid-air while they still had time.
Jump Start: -10. The default was great, but a little less wouldn't hurt.
Max fall: Default. It's fine as it is.
Just as a side-note: This is a great idea, allowing users to look at the physics of a game before you publish it. Good luck with the final product!