The owner before me was a do it yourselfer and updated the plumbing and wiring.

The best way to do this is for you to get it under contract (or an option as @Wayne Brooks said. 

So rather than spend a bunch of money and bring in a specialist inspector for all the different trades (electrical, plumbing, HVAC, roof, etc) you can bring in a generalist at a fraction of the cost to evaluate the whole house looking for a broad range of problems. 

Steve James - James Contractor Services. 

I also have a contractors license and a Construction company.

In that unfortunately (but potential) situation, you end up having to bring in another contractor (who will get paid), and then still have an equity obligation to your friend.In my experience, partnering with a contractor who brings nothing to the table other than their contracting skills is a situation where the investor has a whole lot to lose and not a lot to gain.

If the contractor is unfamiliar or uncomfortable providing you with a fixed price quote ... should this be a big red flag about the contractor?

Managing and maintaining contractors within budget, scope, and schedule is something you have to learn by doing.

I am a general contractor and have flown him to Texas to do electrical work as well. 

Can bring my lender friend and maybe a contractor if needed and his schedule is open.