So half the profit is tax free and half is tax deferred. 

Economies of scale will be magnified if the units are in one place, however assuming you want a nicely maintained property you may lose some efficiency in a rehab, this is because many large apartment buildings have a lot of deferred maintenance and have not been taken care of by the seller. 

Earnings inside a self-directed IRA are tax-deferred not tax free.

The Solo-Ks would use the 55k of yearly tax deferred contributions to buy more rentals using 20% down-payments (or as little as the bank will let me put down without going below 20%, don't want to pay PMI) and would be exempt from UDFI taxes.

You can't commingle the two.I'm not an expert on financing so I'll defer your first question to lending experts.Regarding investing with your 401k: you are not allowed to provide personal guarantee for the loan in your 401k, therefore you must use non-recourse financing.

Opportunity zones allow investors to defer their federal taxes on ANY CAPITAL GAINS until December 31st, 2026, reduce your tax payment by up to 15% when it’s due and pay as little as zero taxes on potential profits on the properties that you purchase in these zones if you hold the property for 10 years.What does this opportunity zone / opportunity fund have to do with Syracuse?

We should have about a $150k deferred gain.

Make sure that part of Wareham is on town water and sewer, and check with them for average annual billsYour insurance estimate (except for flood insurance) is likely high:  Office buildings don't have families in them overnight, so you might find your Business Owner Policy is under $2000/yearLook for deferred maintenance on major systems, which with 10 spaces will likely be your responsibility, not the tenants'And the bigger issue:  Demand for office space in general is on the decrease, with more businesses shrinking their office footprint and allowing workers to work from home.  

.- Going to have an engineer and contractor coming to give their opinion and hopefully a repair estimate, but in my mind the damage is more likely caused by deferred maintenance such as the downspouts and lack of gutter cleaning than the age of the house (saw already about 12 houses in the same neighborhood, all with stone foundation but none seemed to be in such condition.- My inspection period is ending in a week?

I'm aware that if a person gifts an asset, the beneficiary has to pay capital gains on the asset, but if they were to put it into an O-zone, those taxes would be deferred right?