If the roof is leaking on the mobile home , and its been leaking for a long time , you are looking at a lot of work and money . 

Also had a second floor leak with pools of water on it, soaked it up with a towel and still good to go.

However, some local jurisdictions may mandate it.Additionally, bedrooms must meet certain electrical outlet and lighting requirements, cannot have openings directly into a garage, and with some exceptions cannot contain gas appliances.

It is my understanding that you cannot use the ADU for short term rentals in Los Angeles.https://therealdeal.com/la/2019/10/29/while-you-were-sleeping-la-bans-granny-flats-as-airbnbs/If you make the ADU all electric (like I did on mine), then you don't need to worry about splitting the gas. 

I had a plumber refuse to use supply valves because he couldn't verify that they were new and so if there was a leak he couldn't warrant the work. 

I do live close by to a school, hospital, grocery store, gas station.

Other STR related expenses such as electricity and gas are generally more investor friendly and bonus no sales tax in Oregon.- Distinguishably & Scarcity: One challenge (and opportunity) of investing in Oregon is healthy and happy properties.

However, minor cosmetic repairs or repairs to personal property cannot be deducted such as paint, replacing broken hardware, fixing leaks or holes, etc.(2) If you have other types of investments (e.g., stocks or mutual funds) that are operating at a loss, if you liquidate those investments to take a loss, you can use those losses to offset your capital gains.

A month later I tried to turn the gas on and put the service in my name.

Your local S8 Housing Commission should have an info sheet on their website that shows their deductions if landlord chooses not to include electric, gas & water.Even more critical, your $680 mortgage amount, that you appear to be comparing to the S8 rent, should include ALL the other housing ownership costs: property taxes, insurance, vacancy/tenant nonperformance (S8 tenant may have to pay part of rent), maintenance & miscellaneous.Suggest you use the BP Calculator for this.