Since this is a rehab, you shouldn't have to worry about offering a builders warranty but here's some things I've become accustomed to doing to make the warranty, sale process and transaction process easier.  

That is not everyone's thought process but it is mine. 

Due to item 1, adding an ADU can require years to start achieving any return (once the accumulated cash flow recovers the initial negative position).4) Adding an ADU is a slow process.

I found an article on him and there has never been a success story. 

Successful realtors prospect for listings using the same methods as investors.

With a passion for finding undervalued properties and transforming them into profitable assets, they are eager to learn, grow, and build a successful real estate portfolio.

He brings ideas and solutions to issues that come up during the process.

Successful individuals must learn to accept uncertainty, maintain a flexible mindset, and continue to invest.

Having a GC that will provide good documentation, itemized receipts, etc. will make the process much easier I've noticed. 

How much will depend on how well their processes are designed.