It is an older building, early 1900s, and I can foresee some major repairs coming within a few years if not sooner.

We got the house dirt cheap, no utilities were on the majority of the rehab and we replaced everything.

That's great, but if something major goes wrong, they are sh*t out of luck.I really do not have an answer for you. 

15.3% Self-employment taxes is a lot.Scenario 1 - You do a cost segregation study in year 1 and create a huge loss to offset your other income, great for year 1.Horrible for years after 1 as you used up a majority of your depreciation and now your net income will be subject to 15.3%.If your depreciation is mostly used up and don't plan to have net income, your business is not profitable.Scenario 2 - No cost segregation study is done and your depreciation is calculated over 39 years(low depreciation rate, you will likely be paying some sort of net income subject to 15.3%.Maybe not in year 1 if you have a lot of furnishings installed.

This is not first time I read 30 mil apartment, after they purchased they found major plumbing issue, cost to replace all plumbing: 5 million.

Of course, I'm one person and they're a major corporation.

The major barrier to this would be if you are living in one side of the duplex and have an FHA loan on the property.

A majority of investors that come to me for a DSCR loan usually add someone for a similar situation.

The major factors like the roof, furnace, plumbing, electrical upgrades, and foundation repairs are all examples of costly expenses you'll want to inspect before closing the deal.

You should still get a mortgage statement, I don't see anything major you need to track here (missing your entire context please keep this in mind).