I will plan to reach out to in the future to better connect.

This is a REI site, and I assumed he was talking about property management after construction also assuming he was building potential rentals. 

I've helped a few dozen buyers purchase in this market and we've never paid a premium for future revenue.

Hi Eva, Typically the lender will underwrite the loan as if you used the full line of credit so it could potentially change your debt to income ratio. 

I’m a new investor, looking at a potential duplex of 2601 sqft total (3 bed/1 bath each unit).

If the buyer did not close or fulfill the obligation then seller could potentially sue for damages - see this more often in wholesale deals.

Maybe I'm missing something, but to me, it seemed oversaturated and this crushed the potential returns.

This requires an income that rises faster than inflation, or you will not have the additional dollars you will need to pay future inflated prices.What causes rents (and prices) to increase?

MHU will proffer only the TOH type of park (less hassles, easier to manage, etc) but there is potentially bigger returns if you are willing to deal with POH rentals.  

That $140k could be used to buy another investment immediately.Don t worry about future reduction in deductible expenses.