Need Suggestions: Building HV buggy

[tom255]

I have Kyosho MP777 buggy, its laying somewhere under bed. I dont want to run nitro much so thought maybe to try out HV conversion.

I want to go budget and dont want waiste money too much.
First plan to use: Sentilon/OEMRC/Turnigy 100A 12S ESC (go around delay to set motor to spin a litle bit on neitral position using "Tekno" clutch)
Use mech. brakes

And now need suggestion about motor. I dont want to spend a lot of money on that and advantage of HV is low current=low heat.
What you think is it worth to buy low KV cheapo feigao type motor? like 15XL
or maybe something smaller L cans? or maybe some other cheap alternative?
Second suggestion need about battery: I have 2x2500 4S batteries.
Maybe to serialize them and get 8S or buy additionaly 2500 and put it also serial to archive full 12S advantage? Is it worth go over 8S?
Third question about UBEC, is it availible somewhere that can handle 12S lipo or hook usual bec to balance tab of one battery?
Sorry for my English i hope you understand me
Thanks