You should always look for Tax-Deferred and Tax-free methods to Invest.

It's a former adult care home, so the layout is shared bathrooms, and this would allow me to not have to change the plumbing layout while offering a competitive price-point and unique experience to travelers.

You can sell on financial method because there is such short demand there is all but no comp's to use for comp method, and if selling as turn-key, yup, financial method will be your friend for sure. 

What tools or processes have you implemented to estimate rehab costs more accurately and avoid scope creep in BRRRR projects?

Lots of methods and resources.

Obviously if you’ve done this before you likely have a method you prefer for dealing with these types of things.

After about a month of no response on FF I switched my method to LTR.

@Abigail King I mean, I wouldn't classify it as "creative financing" as much but my favorite strategy has been the BRRRR Method for many years.  

I've done extensive research into the options and a lot of the paid options seem to focus on teaching specific investment methods.

I plan on taking some introductory classes for plumbing + electrical + carpentry + ???