Our contractor was fastidious about sealing off rooms and taping unused doors, but we still found several rooms full of dust.

You can offer to escrow some money for 12 months for the repair and if it is not done in 6-8 months, do it your self or have a contractor do it...  

6) electric bill of $25/m?

If a detatched ADU is built in the backyard, it would need to have a new 100 Amp electrical subpanel right from the main electrical meter installed by the utility company.

I didn’t put anything for the garbage electricity etc.

It was brought to the sellers attention who advised he would repair the garage to stop the flooding (he was a contractor).

As long as you gave yourself that option then just take the time to verify the numbers, if you have a relationship with any other local investors or contractors ask them to come walk the property with you and get some input. 

I'd do some resarch on the home itself (see if she'll let you view it and bring a contractor or flipper, hopefully you know one who will go with you) and do some research on what other properties (both vacant lots and homes) are selling for in the area. 

Hi, I have worked with a contractor for the last 2-3 years in TX and although he is slow, I stuck with him for convenience and dependability.

@Terri David you could possibly "hire" someone, for reduced rent, to look over the property and do showings, meet with contractors, etc... on a smaller building, but you'd still need someone to manage payments, marketing, tenant screening, etc.... it could save you some money on the management side, but you still need some type of management company, if you didnt want to do it yourself