Growing a roster is a great way to create predictable revenue too.

Time is your friend and it goes by faster than you expect.Personally, in my 15 years of investing, my biggest mistake with rental property is that I sold.

The biggest thing is communication, keep it touch with your tenant, make sure you emphasize that you want them happy with the property and that you need to know right away of any issues with the property.  

Buying 2 investment properties would likely bring in more revenue and equity than renovating an ADU. 

My biggest piece of advice is to learn from the experiences of others.

It sounds like the biggest issue with BRRRR in your opinions is the refinance portions?

In larger mutlifamily properties I typically increase my existing expenses (non-mortgage expenses) by the same growth rate as my revenue.... assuming I have up to date and accurate existing expenses.

I already have a couple potential deals, but the biggest hurdle I'll face is finding a private money lender who's willing to lend to someone with minimal experience.

In general, developers will model revenue with SAM or an equivalent tool for non-dispatchable production.

 - I saved my biggest reason to last.