I have simply been around this business for far too long and I understand fully the technique, purpose and use of guarantees.  

Does anyone have any tips or techniques you use to determine ARV?

While leverage can typically be quasi-tailored for an investment's risk-return appetite when securing new financing, buyers are limited in their leveraging options in a loan assumption.

I has the basics and I tailored them to my needs.

By using this technique you will never need a proof of funds letter. 

I have to tailor my screening to get the most suitable candidates as possible since I am out of state and have to rely on external services (per fee).

And if you can't find any recent sales of ADU properties, there are other techniques you and they should be using.

Things like investment calculators, once you have a solid understanding of investment fundamentals can be replicated on Excel, and tailored more to our markets. 

Tailoring content to each platform's audience is crucial—for instance, more professional content on LinkedIn and more visual, engaging content on Instagram.Bigger Pockets: An invaluable platform for real estate investors.

You will tailor it as you learn more about the process but on the surface its a good start. good luck