Well the first thing is to decide to use the models we have in game or create own. I recommend to start with existing Terran models.
Power: Each power plant (Supply depot) provides power, each structure consumes power. Units do not consume supply.
Check campaign called "Marauders" to see how C&C style resource gathering system was made.
The UI sounds most complicated. At least you can hide some parts of UI with triggers. I believe it works quite fine even without C & C style UI.
Do not start the project with too big goal. Make the parts of C & C that you can make easily.
Oh, and check this if you are not familiar yet: http://www.openra.net/
Custom Campaign Initiative is project that gathers best single player campaigns and their makers together.