Please help me with deal analysis

[Joel Packard]

Here's the deal. I have a seller that has 8 lots with old mobile homes on them for sale. We have an agreement (verbally, going to get it on a contract tomorrow) for me to buy them at $70k each. He will carry a note on all of them. $56k down,  7% interest only payments with partial payoffs and releases as I resell. My plan is to pull the old mobiles off and have new mobiles installed and resell. My total costs to have the new mobiles installed is $110,500, with a sale price of $215,000. I only have the cash to install 1 new house at a time, but the old mobiles that are on the lots now have tenants currently in them paying rent so I will actually be cash flow positive on the lots that I'll be holding. A pretty conservative estimate is that it will take me 4 months for each lot to sell, so it'll be a 32 month project. In my projections I have an increase of 1% in sale price which I think is reasonable (3% increase per year). 

When looking at risks, I think the biggest risk is a market downturn. If this happens my exposure is only to the cost of one new mobile at a time, so I could drop the price to get it sold quick and then hold on to the other properties as rentals until the market turns around.

I've done a lot of thinking about this, but I'd like to know if anyone sees anything I'm missing. Please shoot holes in this deal for me. What have I not thought of?

Thanks-Joel