They used different strategies: house hack in CA, STR, buy off market, buy OOS, SFH, multi-units, buy large apartment complex with other investors, etc.Thoughts on 1031 exchange to DSTs to try be more passive (no more dealing with PM, renovations, repairs,  tenant issues) but I've heard the money is trapped for 2 to 5 years depending on the operator, still researching DSTs. 

We've done this on some of our apartment complexes because two medium-sized heaters are easier to replace than one large one.

I can totally appreciate what @Keith Leckey @Austin Mountain have described regarding their personal experiences and the fact that the three of us have given you very lengthy responses to the realities of Section 8 should tell you alone the complexities that you will no doubt be dealing with if you care to enter into the program.  

I am considering branching outside of Utah for some apartment complex purchases and this is a major factor in my location criteria.

We've seen houses with a purchase price as low as $150,000 benefit from a cost seg study, so I wouldn't say it's reserved just for large multi-family complexes.

It gave us a really nice nest egg to roll into our 16-unit apartment complex that we own and manage now. 

If you can't manage a rental or tackle a basic remodel there's a strong chance of failure jumping into complex strategies.

I have a 16-unit apartment complex and have made every mistake in the books.

Keep in mind once the ADU is complete your old unit will most likely become RSO which will mean any alterations are much more complex and limited.The downside of this route is that if you build the ADU now and your old house is built before 1978 you cannot split the lot because the old house cannot be on its own lot once it falls under RSO.

How old is the complex?