Thanks, sundaydoug. We are definitely not looking for smooth. We routinely ride singletrack and forest roads in Ringwood, which is a definition of not-smooth. We can do uphills unless they are really steep. It's still difficult for my son to handle rocky ascends - this is where I push him from behind (meaning he still has to pedal and choose his line) or he hikes a bike (as a last resort I carry his bike). So everything on the intermediate side is okay, except really long technical uphills. As a reference for "technical": race trail in Ringwood is currently as far as we venture, but on average prefer something a bit lighter.
I have no idea where to park - anywhere, I guess, depending on trails we are biking. How long? Hard to say. 3-4 miles depending on terrain?