Belts shouldn't have any slowdown or length penalty: it doesn't really make sense and it doesn't help the gameplay. Adding motors sounds like a nightmare.

They really just need an electricity cost, but have it so the belts connect to each other so as long as one is powered, all of them are powered ...

This isn't a real balancing issue: generating heat via electricity via coal-fired turbine should be less efficient than generating heat by burning coal directly.

The 50% boiler efficiency is meant to show energy lost in the electricity-generation process - wikipedia says [uncited] that stationary ...