There are mortgage recast calculators online or you can reach out to your lender.P+I payment will go from 2155 to ~1800 given the numbers you provided.

Also, their past decks don't provide the type of basic information that any sophisticated investor would need to evaluate them (like skin in the game etc.).

Some mortgages also don't allow a second lien on the property, so how do you provide the seller with assurance?

The loan is listed on the HUD and they provide lender's title insurance.   

Be sure to check out the free tools BP provides to help analyze deals you may have and also market insights.

I recently looked at an existing STR, but either the seller did not track the expenses or they did not want to provide them. 

These I have found are real, striving parents, working their butts off to provide the best housing and school system for their children.My ethos in this approach is exactly why we at LaPlante refer to them as Residents, as we consider "Tenant and Landlord" to be dated terms and rife with negative emotion.

These areas tend to attract high-quality tenants and provide consistent passive income, which is a great foundation for building your portfolio.If you’d like, I’d be happy to share some insights about these types of markets and why they’re appealing to investors.

Great information you provide here.  

You can't decide which one to choose based on the minimal information you provided.