It seems too simple to not already exist, but I've had zero luck researching it. 

Unfortunately, the existing Roth would have to stay separate, but if your overall financial strategy is to employ Roth and Traditional tax strategies, the Solo 401(k) may be a good choice.

Spend your time learning real estate instead of the lending rules and regulations.

It took a while to figure out what the issue was, but Zillow had taken my Unit 1 listing and combined it with an old Unit 2 listing and created a completely new listing that has never existed - and both of our photos were right there in the fictitious listing.

@Do Luong Check with your local zoning office to see if and what you can put on your existing land.

If it's under contract, I suppose you could make a backup offer but that backup offer doesn't go to the lender for review/approval unless the existing offer is no longer in consideration.

I have rental income in 2018, too, but that's obviously not on a tax return yet.I don't think either bank was interested in a HELOC against either my existing rental property, or my residence... they were trying to send me through the conventional mortgage route.So... what is my next step? 

Does your lease state the tenant must comply with any HOA regulations?

My question is this:If I sell 1 of the 4 duplexes can I 1031 exchange the $ from the sale back into the existing commercial loan?

If it's a forelosure you may have to honor the existing lease for the remainder of its terms , some states allow for 90 notice to amend