are mountain bikes allowed on the trail?

Yes indeed

You can ride in from the west side of the preserve and then towards the south along the powerline. But it ends at a locked gate at the top of the hill. Stairs, unrideable in either direction to the northeast. Wife and i ventured around a bit in the fall. Definitely short loop/section.

Yes. Sometimes I see guys on bikes in there. Usually the homeless who stay in the area rather than recreational bikers.

Its not really mountain bike friendly. Fair short and lot of stairs.

Yes