You can park at the art museum, along Westfield (near Illinois) or in Braod Ripple. The path is easy to access and easy to ride. It does get crowdedd during peak hours though.

Crushed limestone is a pretty easy surface to ride on except, perhaps, when it rains. I doubt you'll have any problem with it, either in terms of handling or your hands.

As for deep gravel (as you asked about in another thread), that's tougher as it can give anybody fits. I'd suggest getting comfortable first with crushed limestone and dirt before giving gravel another go. I'm sort of in your shoes in this regard as I've yet to learn much about MTBing. That said, I anticipate that MTBing will help me learn to move around the bike better, which would likely help on a road surface like gravel.