We had looked at rehab opportunities for a couple of years but the numbers never seemed to work especially with the "unknown" factor.  

All unknowns for me, too. 

It's easy to predict short term rates are going to rise, and directionally we know where long term rates are headed, but the magnitude of those changes is unknown.

I know that repair value (barring the inevitable unknowns) can be influenced by condition of the home and property, area similarities (meaning, if your comps have granite counters, then your flip needs to have granite counters), and budget.But, what do I really need to know?  

Can't predict the unknowns. 

For some reason, they will be great for 1-2 years and then something unknown happens and they start to fall apart.

Trying to make a silk purse out of a sow's ear is difficult, time consuming, has unknown results and just doesn't merit attention.

While we have compliance issues here, there are also liquidity issues unknown to investor/brokers getting involved in pooling money, it will be a matter of time before someone will need to be bought out and the broker better be in a position to do that, most won't be.The arrangement will give indications of a broker needing liquidity as well as other investors. 

When you have any of the three variables you can solve for the unknown.

Make sure the finances are solid, that will help alleviate some potential unknowns.