It's a risk, of course (because they may not sign your lease or move in on 8/1), but to offset your risks, here are some tips in general terms. 

I'm looking to purchase a single-family home in the $500k-$600k range with a long-term hold strategy.

The negotiations were quite difficult to find the terms that worked for both parties.

If not I will try to refinance and then either pull the trigger on furnishing the home for STR (cleaners and handymen were hired/ interviewed on the trip out,) and still have the boots on the ground in case of emergency.. or just long term rental and refinance, repeat…Not a perfect deal, but I learned a ton!

That's standard beginner terms. 

Brokers (versed in these development deals to help you negotiate the right contract terms), Lenders willing to fund a construction and permanent loan, architects & engineers vs in land development to help site plan the project, contractors to price the project to help dial in your UW. 

It's just my husband and I and we are finally narrowing down our niche to MHP's and long term RV parks.

We are thinking very long term, so in order to cover bases regarding potential deaths, wanting to pull out, or being unable to afford the investment it seemed like the best way to go.Really looking for some general advice is there is any, we feel we've googled and researched everything that will apply, but are there anymore pieces to be aware of? 

This will be done as a "rate/term" transaction, so better rates than a cashout transaction. 

I own a beautiful piece of land in Carson, WA with much potential for short term rentals.