Free Advice: Create two LLC's one for flipping and one for your passive as this will prevent domino effect if one aspect fails and make sure you setup proper firewalls to prevent commingling funds. 

My question is, are there any rules preventing me from working exclusively with investors?

It's better to prevent any "targeting" in the first place! 

It can also be used in a wall near pipes to keep them from freezing if freezing is a problem, but it will provide heat that keeps the building warm and will prevent freezing. 

There's a similar property that just went under contract and there's potential to make a good hunk of change with the one I'm looking at, but didn't know if anyone had experience with a ROW preventing a sale or  being able to get a good market value for it.Also the adjacent lot the ROW is shared with does not appear to be inhabited.

Either you sell at a higher price and give him the controlling unit or somebody else sells and you're left holding the bag.This guy wants the whole building to take it private and convert to apartments.Somebody else will stand in his way and prevent that, but their life will be miserable. 

There are self rental rules in the Internal Revenue Code to prevent this. 

I told him he's in violation of the lease.My insurance agent told me to include me as an additional insured in the tenant policy to get notified and prevent problems related to cancellations.

Talk to someone who knows about water entering buildings and preventing that, and listen to their advice.

The state came in and said we needed a back flow prevention for the water system.