Hi Dave and
to the forum, whereabouts in the UK are you located?
I think rear wheel drive is the best option, especially for use on off-road tracks, and I would choose the freewheel version along with a suitable freewheel with a wide gear range
(11-34) even if it means replacing the gear change mechanism and having fewer gears on the rear.
I received a pre-production cassette version of the MP Edge and was not happy with the axle attachment, which is why it has not been fitted to the bike that was purchased specifically for it.
I am still waiting for sufficient spare time
(and renewed enthusiasm) to modify the axle to allow a dedicated torque arm to be fitted, as shown in
this post.
I'm also hoping that I will be able to modify the axle
(as shown below) to allow the bike's original quick release skewer to be used:
If my calculations are correct, the quick release skewer should be able to clamp the axle tight enough to prevent any vertical movement within the dropouts under full power.
Regarding the clearance on the front hydraulic caliper, you may experience a clearance problem if the hydraulic brake caliper has pistons on both sides of the disc
(or a very thick casting on the non-piston side), but I don't know what size gap there is on a front MP Edge.
A pair of suitable torque arms should also be fitted to prevent the axle from breaking the fork's dropouts.
Alan