Are there any mountain biking trails here?

Not that i had seen . I would suggest going to the web site or call to get the correct info

Yes, Jones Mill trail is a mountain bike course. It is not at the main entrance, but is off of Barnett rd south east of the main entrance. They are currently adding on the the existing 3.5ish miles

I really thought there were, like to the right before you get to the loop/ boat rentals, there's a playground to the right and bike trails, i think, to the left.

No

Not sure but I would check their website

Yes, the Jones mill trail is for bikes, trailhead is off of Couchville pike.

I'm not sure but you can call or go to web site