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

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. 

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

As long as the custodian company is responsive I wouldn't worry too much.Do your due diligence and make sure the custodian company is legitimate.

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

Lots of methods and resources.

In the case of a HomeStyle Renovation loan, your lender might have added PMI at the time of the loan because the LTV was higher than 80% at the time of the initial loan and renovation.PMI Removal After Renovations: If your LTV has dropped to 73% after the renovations (meaning the value of the property has increased substantially), you may have a legitimate case for PMI removal.

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.