I was going to go the lipo bms route but after considering the main fail point on chineese ebike battery's is the bms going bad and draining a cell down over time I thought I run naked but monitor voltage of pack and cells as well as watthour so I can build an accurate picture of charge state.
With 18650 a bad bms creates a bit of heat as the battery depletes but no major fire unless there's high discharge parralled cells but with lipo if the bms keeps on draining them they will get hot and catch fire the larger ah cells can really get a barbacue going so make sure the bms is good quality stuff.
Nice build though it looks awesome nice and clean, i bet it weighs very little and with the regen I suppose it can cover a fair distance, With that bms attached keep the battery separate in the corner of the shed isolated from anything to save burning the ride out and anything next to it.
Scrap the cheap bms get it 2wd and run a shunt with volt amp meter display with rc battery alarms on the balance wires and charge with a server psu and dc rc charger ?
There's a decent display from China cheap as chips with a shunt
http://m.ebay.co.uk/itm/DC-120V-200A-Wi ... 2278832443