The Manistee River Trail can be a great fit for many different levels of runners. You can run this trail from start-to-end if you have a group with multiple vehicles. You have the choice to run all 10.8 miles and then retrace your steps back to your vehicle for a 21.6 mile run. My favorite thing to do is to park at Seton Creek campground, run all the way down (10.8 miles) to Red Bridge (reserved campsites available) and then run up the other side of river on a section of the NCT (10 miles). Then you can cross a suspension bridge and retrace the first 1.5 miles or so of the MRT back to your vehicle.
There are many marked campsites along the MRT and many more locations that will work just fine if you head off the trail into the forest. Water from the river is never really far away from this trail. The NCT side of the loop has few spots on the southern half of the loop that have water access and need to be planned accordingly.
The MRT has a few small waterfalls along the trail which can make for a great place to sleep if that sound does it for you. The terrain is a singletrack that is a bit rough at times but well maintained. It is not terribly uncommon to need to step over small trees or run through some mud at times.