There is a 24-hour race on Saturday/Sunday so you won't be able to ride there unless you're in the race.
To your questions:
- get a map from the gatehouse ($4 fee to enter)
- the black arrows is the singletrack, though it includes double track
- if you park by the chalet (directions on map) the singletrack starts out front of the chalet and follow the signs (getting lost is fine, place isn't that big)
- I've never seen a hiker on the singletrack
- the singletrack is loaded with rocks and roots, but it's plenty hard (and fun) in terms of climbs and twists
If you've planned a trip here and still want to ride, Mansfiled Outdoor Centre is about a 1/2 hour drive north and there are other places within an hour drive.