What I would add:

1.Customization. Not only weapons, but increased armor plates, better motors for speed, shields... basically what can be placed on a modular armor and something more.
2. Remote control. Maybe an optional module for remote control. You select the mech from map view and control it ...

I like this idea.
And i think it will be nicer if we have some tools or buildings that can actively absorb pollution (like an air filter) at the cost of power and some resources (like plastic).