Just thought I'd put in my 10 cents, AAI Programmable Vehicles seems to do everything you want your harvesters to do, perhaps a collaboration would save you some time reinventing the wheel? Also this seems to be in line with the Tiberian Dawn mod, perhaps some optional features/resources/techs might be viable.

Good luck with it, loving the concept :)

After trying with AAI I spotted it automatically adds it to the list (must be an embedded feature for all vehicles).

it's an AAI feature, it sort of works? Mining is spotty at best, though.