Pretty agents who like to sell pretty houses don’t necessarily understand the investment strategy that you are employing.

However, recently a good friend of mine from church (who happens to have an extensive experience in RE) offered me to partner up to help me start and without me having to put any money, just asked me to contribute to him by finding a low cost deal, help with the process and he promised me to split profits equally if either selling or holding.

Once rehabbed, what disclosures would I have to make if I were to sell it as a flip?

OrSecond: buy a single-family fixer upper (400-500k) home, live in it for 2 years and either sell it to avoid capital gains tax or rent it out. 

I am selling my long term rental and hoping to move into multi-family investing and learning about finding investors.

Some areas here may have rent by the room ordinances for non-family so you would want to check, but single-family homes in the same areas should be selling as hot or hotter than multi-family.

You can list the property as a "net listing" and take the difference over what the seller is willing to sell for that way. 

What are the PRACTICAL remedies if he does indeed decide not to sell or show up at closing.

Its a terrible deal, max I would pay is 250k, there is a reason its not selling, 

B) if/when I choose to sell it gets a premium from buyers.In Cincinnati, we have a LOT of older homes (think built in the 1920's - 50's).