I would not put any energy into this aspect. the only other way to get one is to take title subject to a 30 year note that can happen as well. 

In the process of BUYING a PURE Option to buy a SFH subject to an existing loan (at a lower fixed long term interest rate)Let say the OPTION "Strike price" to BUY the property IF or WHEN the OPTION is EXERCISED is $300K The seller wants $60K to sell us the OPTION.

It's way too hot for hiking in the summer, and ugly in the winter once all the green is gone.

If you know of any good resources—books, threads, podcasts—on the subject, I’d also appreciate the recommendations!

As for a information to specific grades for neighborhoods, you may struggle to find that as it can be fairly subjective.

They underwrite much like conventional loans and over condition for things that have nothing to do with the subject property and often make a mess of the entire DSCR process. 

@Chris Berry - I wrote a blog on exactly this subject.  

THEIR PROCESS may have been fine a year or two ago when rentals were hot.

Does anybody have any advice on this subject, anything I should watch out for, is a lawyer necessary, does everyone have to sign the deed, or is it a straightforward process I can do myself?

Imagine trying to ask an owner permission to add on hot tub or high cost item just so you can compete.