From your first call (off market) to a signed PSA how many calls do you take.

The experience of the housing provider is going to be the real challenge to getting you a set of keys to move in with...they have to qualify, pass inspection, sign a bunch of paperwork, and finally lease up and send everything into LMH. 

Does this middle man make a percentage or profit by bringing us to the developers, if we sign through them, with one of ‘their’ developers?

You’re acting as the assignor, so once the assignment agreement is signed, the buyer takes on the financial responsibilities outlined in the PSA, including the EMD submission.

Most people don't have the patience to do things right and all they see are dollar signs.

I was sent an addendum to extend the closing date but did not sign it.  

If you end up giving them the notice to vacate do not offer the option to sign a lease.

Several things to consider: 1) One of the main purposes of segmenting your assets into separate LLC's is so that your personal net worth or equity in other business ventures or properties isn't exposed, so unless you have a high net worth or a lot of equity in a property, it might not be worth bothering going the separate LLC route, especially when it restricts your financing of the property.  2) Most any commercial financing you get from a local bank for a small property is going to have recourse anyhow and require that you sign a personal guarantee, so you're still personally on the hook to the bank even in the case of a commercial loan.  3) If you're a newer investor and buying a deal that's tight on cash flow, or if you don't have a ton of cash sitting in the bank already, your greatest risk factor as an investor is your investment failing economically due to poor financing terms or not operating the investment properly, not because you get sued. 

@Jesse Jones-Smith, I'm a lot like @Nicholas L.. 

The assignment agreement addendum was signed a few weeks into escrow.I was not worried that this would trigger the seller to back out.