It's easy to obtain, costs very little, and doesn't require extra, on-going effort to maintain. 

Do you know trustworthy contractors that could complete the required work?

You also may be required to have certain drainage features built into the land, building setbacks from the curb, number of parking spaces, number of handi-cap parking spaces, space for trash, et cetera.

It might be cracking and heaving inward which might require both dealing with exterior ground moisture and also stabilizing the foundation from the inside with one of a few options.

Depending on the financing in place on the main residence, you may be able to “sell” the parcel with desired ADU to an LLC and then “buy” it back from that LLC using the 1031, but it would no longer be an ADU unless always sold together.

This investment in your property could be justified by the increase in rental appeal and tenant satisfaction, making your property competitive and desirable in the rental market.Ultimately, the choice should align with your investment strategy, your relationship with the tenant, and the overall condition of the rental market in your area.

Have several SFP but want to expand.Nothing specific as far as requirements as long as the deal makes sense and you don't have to squint and hope the numbers work.I have 2 Equity Partners looking to do deals but they have a little bit of a gap in what they are looking for.

Very humble, hardworking, blue-collar family and they happen to grow up in a part of California that is highly desirable now.

the book in the bp bookstore. i did the rookie boot camp 2y ago that i imagine this book is kind of based around, and one of the first steps was picking your strategy. the tough part is: THEY ALL WORK. but they all require different skill sets, different amounts of time, and will create a different-looking life for you once the ball is rolling. you have to lay out what skills you have, what you do and don't like doing, how much time you have, and what your vision is for your investor-life 5y down the line, and choose the strategy that aligns best with those things. 

As for the downpayment, the lender might be requiring more down in order to meet DSCR requirements.