Or is there something I'm missing from the complicated section 8 process. 

Problem solved.It isn't like a fridge or washer take a complicated hook-up....just plug 'em in.

To be sure, we can complicate the argument by introducing the tax advantages that real estate investment such as depreciation etc…but we won’t go there now.so, if we assume that the appreciation of real estate in general is going to be negligible over the next several years, as a prudent investor you should look for properties that can cash flow at the minimum rate of return equivalent to or better than the rate the bank would give you on your money. 

Are there any building regulations for quadplex that are more complicated compared to duplexes?

The ROI on solar is more complicated than a one line answer on a forum post. 

Sounds overly complicated with little-to-no benefit.

Assuming that is close to correct, I think the owner will likely find this complicated and make it a hard sell.  

Complicating the matters are 3 tenants, non of them paying rent. 

It may play out well for you, but the details are tricky, and the adjustment procedure is complicated.

you are not alone nor dumb, i read an American study that 40% of home flippers lose or only break even on their projects. please talk to an attorney with bankruptcy and real estate experience before filing as could have long term complications.