I have a subject to deal in Dallas County where I'll pay the back payments on the loan to take over for the current mortgage owners.

If you had built a separate ADU and not converted the garage, you may have been able to use the garage for the JADU.3 & 4) "multiple accessory dwelling units within the portions of an existing multifamily dwelling structure provided those units meet certain requirements; or (4) not more than two accessory dwelling units that are located on a lot that has an existing multifamily dwelling, but are detached from that multifamily dwelling and are subject to certain height and rear yard and side setback requirements."

Hi all,I realize this is a really detailed subject that's impossible to explain in 500 words, but does anyone have any tips on estimating rehab costs?

@Adam Dow TONS of info on this subject right here on this forum!

There are tons of books and information on the subject. 

So when you owner finance the property to someone Subject To the existing mortgage, you run the risk of your lender finding out and calling the note due.

Then you can record your expenses there and it makes it easy for you and your CPA.Regarding startup costs versus expenses, there are plenty of articles you can find on the subject with a google search.

Do you know who is the #1 expert in SUB2 deals (also known as "Subject to")?

The only income that is taken into account is the subject rental income. 

“One reason for the request is that GSEs Fannie Mae and Freddie Mac are not subject to this rule, under a condition called the "QM Patch."