Does anyone have experience building waterfall real estate models? 

I am looking for insight and expertise with the HVAC system, because I am newer to real estate investing.There is currently one natural gas furnace in the basement that pushes air to all three units and floors.  

Discuss with them a model where their job is easier and they win and you both will win.

Know where your business model is exposed and make plans to mitigate that risk if something should happen. 

no matter your strategy, I would find someone with expertise in that area and ask for specific advice.

@Michael TruebaMichael: Your best bet would be to call a couple property management firms who have expertise in the asset size that you're pursuing and ask them what they're seeing across their portfolios.

While his business model wasn't completely interesting to me in a practical sense, I agreed with some of his concepts.

Hello Jay,it copies and paste a little backward.. but by my sending this in and subsequent meetings with the state of Oregon investigators its clear that assigning contracts with no intention to buy IE its your business model and advertising in ANY manner a property you don't own is simply illegal in this state.. 

If you decide to file as an LLC, I can certainly lend my expertise on that matter.

The cost of turnover/vacancy should already be baked in to your business model.