Cutting to the chase, I have a long term vision of starting a Design + Build + Transact firm.

Unless there’s some other personal connection and you feel obligated to cut him in...

For a stove for safety I would probably go to electric.

I'm sure the other agent would want to know whether a vendor they are vouching for is not cutting it.

If that 12 feet goes through your living space, you are going to destroy all the flooring, cut the concrete and end up with a huge mess to clean up.

Good example, I had a slight pricing and supply chain issue on some needed materials, I could have thrown $ at the problem but instead I made some calls and I bought a partial rail car of the material, lined up my own motor carrier, was able to cut 2 middle-men out of logistical chain, 1 1/2hr drive to rail yard to personally supervise and we got out materials, faster than anyone could deliver, for 30% discounting AFTER all associated costs.

I think you have a pretty good grasp of things, but if there aren't many STR with your capacity you may be under cutting your own prices without knowing.

Preferred return is what you get paid before GP get their cut. 

I was wondering if there are companies out there who work as an intermediary to do that, I cut them the check and they go to the county on my behalf? 

The previous owner scheduled the power to be cut off.