I have less knowledge about Seattle but my oldest friend did a basement conversion ADU in Seattle (I am at her birthday in Long Beach Washington at this moment).  

I mainly invest in SFH because I think the appreciation and total return over the next 5 years is better than MF and it’s actually less complicated but I know it doesn’t cash flow AT ALL and it’s ok, I’m building long term wealth not cash flow. 

If a lender saves you $200/month on the payment but you spend an extra $8k in fees, you didn't get the terms you think.

So, you need to be sure it makes sense as it does not always do so.Also, keep in mind, line of credit are for short term cash needs NOT long term for example a down payment on a property you plan on keeping for the long term.

BP is a great place as long as you understand that most posts containing preferred locations have a strong marketing bias.

Find a lender who understands your long term real estate goals and understands that rental income can help knock down your DTI to qualify for more loans and acquire more properties. 

Quote from @Kai Kopsch: It doesn't matter what Airbnb might say, as a realtor, you have to use the NAR rental contract from you're State and RE Commission or an attorney draft one.Are short-term rentals regulated by that state commission?

I envision offering the full gambit of stay options: short, medium, and long term rentals.

So long as your lease supports it, bill them for the repairs. 

It sounded like another term for assumable mortgage, but I appreciate the clarification.