I used the 75% rule on the income and added it and my DTI without the rental goes from 24% to 38%.Or does it just allow me to just take the net profit of that rental and add it to my rental? 

What is being reported is that outside of those numbers, an additional 70,000 government employees have already selected an early buyout rather than get fired or have to go back to the office. 

Her husband is also a GC who can help build additional units as needed if you get something that can fit an ADU.

This doesn't replace the need for a MSA that will capture additional clauses needed on a Contractor-SubContractor relationship, this is just a project specific form you would use in addition to the MSA (prepared by your Attorney):This template is for informational purposes only and does not constitute legal advice.

Given your experience with RV parks and MHPs, you already have a strong foundation for managing mixed-income streams, which will be valuable here. 

Additionally house tenants bring more of their own appliance, like refrigerator, washer and dryer; which means tenants are responsible for repair and replacement of their own appliances. 

Additionally, the estimate for my tax preparation for this year was approximately $1,000 over the cost I paid last year (including the time I paid for them to correct their errors).

Most likely a "discount listing" Owner pays realtor a small amount upfront to add it to the MLS.

I want to make this a valuable thing to my existing tenants.

A PM offers so many additional services in addition to things you cannot do yourself - like simply having a 3rd party between you and the tenant.