I always cope MDF, or anything. It makes a big difference in the finished product.
I use the easy coper jigs, and a bosch jig saw with a very small blade. You can get exactly up to the line, even me and I have the shakes. (essential tremors)
Ya it takes a little longer, but the results are amazing. you do have to be careful not to bump into stuff with the coped end(s) but other than that I guess it's like anything else you get good at it after a short while.
As for holding up the 16' lengths I use the Lee Valley crown hangers.
You put a screw up near the ceiling about 1" down, then this hanger "hangs" on that screw. It's sorta like a large fish hook with a movable barb.
Hang your crown on that, then adjust the "barb" part up a little bit so the crown is up against the ceiling, then nail off. When you get to the hanger, just lift it up a bit and slide it down out of the way. The screw will not interfere with the crown.
Lee Valley coping jig: 03J75.80
Lee Valley Crown hangers: 03K18.05