Weight. There is a net gain in weight (hardly a secret). Fuel v motor and associated kit. This was known very early on & was fully allowed for in the calculations.
There were many such considerations. (Most engineering decisions involve a tradeoff.)
'A few hundred pounds' Considering the NG hub space available, that would imply motors made out of lead. However be assured the production motors will be robust yet relatively light with a very high MTBF.
Hydraulics (expensive, heavy and require a lot of servicing) is one of the systems Boeing is targeting in
future designs.
I have covered the traction issue before. The plane moved - repeated stops & starts backwards, forwards, left, right, up slopes, down slopes. Traction was sufficient. If it wasn't, Neither the test pilots (One of whom was Air Canada's Chief Test Pilot) or Boeing would not have reported so favourably.