But being as this is the number 1 motorcycle destination on the planet it could still work if it were cost effective for everyone from the investor to the STR biker.

Finally, small increases in dollar amount have an outsized effect on tenants paying lower rent.You also don't mention mortgage details, and at 15% down you will likely have PMI, so just make sure that is included.  

Fantastic way to waste money.

Doing it the opposite way will likely waste time and money, and require you to find a unicorn lot for you predesigned build.If you strategy is to build to rent, than you should focus on that.

Using a realtor will effectively cut your profits.

What is the best and most cost effective way to finish/cover the sad plywood?

Effective January 3rd 2022 they are not allowing STRs in R-1 zoned areas.

If they have never done a MHP loan, don't waste your time. 

The expense is more up-front but is far more cost-effective in the long run.Regarding your specific question, unless they have an agreement with you there is no expressed or implied contractual obligation for you to hold the rent. 

From the agent's perspective, though, I understand the risk and unwillingness to "waste" time if you aren't sure a buyer is truly serious.