The key is getting the education, studying it and eventually learning through experience. 

You can hear real-world examples of how others have built their investment portfolio and (hopefully) learn to avoid their mistakes.4.

@Johnery LaurimoreRecommend exploring as many sources as possible to get referrals AND cross-reference them to get as much accurate information as possible.Check out NARPM.com, BP’s Property Manager Finder, etc.Also, encourage you to learn from the mistakes of others - by reading posts here on BiggerPockets about owners not having their expectations met by their current Property Management Company.

I believe I had a list that was 12 items long.

Learn where to look for the date of manufacture and make the seller send you a photo.

Repairing foundations is a big, big ticket item.  

@Caroline Gerardo is right.Your big bang items are 1) Kitchen and 2) Master Bath.

The SFR + ADU is worth less than a Duplex because the ADU is viewed as an amenity rather than an additional unit so your appraisal will look for other SFRs with ADUs and provide line item adjustments for homes with and without ADUs much like having or not having a pool or a garage.

You can - and should - say no to this tenant and any future renters.Spend some time learning the law and how it applies to you.

Also, learning about creative financing will be a priority.