My current rig is a
26" Full Suspension Giant Anthem bike with a BMC Rear hub motor, 72A Lynn controller, upgraded torque arms and 10Ah Zippy lipo pack consisting of 4 5000mah 25c 6S packs. I put 2 in series and those two in parallel to make a 10ah 12s pack..... .......This setup has plenty of torque and speed for the type of riding I do but I dont think the BMC was setup to withstand 1800w for any extended period. Need something designed for the higher load's.
Your statement is sort of conflicting, but I think you are saying that you are close w/ your current set-up. Given the amount of time and money you have invested, it seems a shame to ditch everything and start over.
Why not add a sm. geared mini-motor to the frt. for a 2WD? Then you could;
1)Install new Halls(avail. @ Ebike CA, BTW), leave the wires alone and use a more reasonable controller in the 35 to 40 Amps range.
2)Stay w/ the LiPoly and use another 2S/1P or 2P pack for the frt. motor, giving you a total capacity of 15 Ah or 20 Ah.
3)Take some of the money you are planning to spend and put it into better whl.s and tires.
Now I know the experts will come on here and say that a frt. motor will ruin the handling and is not needed, but I will say it depends on what kind of trail rider you are.
If you rail the berms, do drop-offs, loft the frt. end alot and generally haul ass, yes, I would say go w/ the mid-drive or a huge hubbie and deal w/ the problems that will arise from using those set-ups.
But if you are like me, have slowed down a little, pick the trails that are not the most difficult and don't try to climb hills that you couldn't walk up w/out to resorting to all fours, 2WD works very well.
More or less, the same rational applies to the donor bike. Your Giant is fine for 'less than all out" trail riding and if the above mentioned whl. and tire up-grades are performed, that could be taken up a notch and flats could be a thing of the past. My experience w/ trail riding here in the desert is, flat tires have been the biggest challenge to overcome.
I've worked out the throttle set-up and the best way to bulk charge LiPoly over the years and could supply some links should this might be an option for you.