Also, Oregon state rent control rules limit to less than 10% per year for rent increases so the under-market unit may end up being under-market for a few years due to legal restrictions.Why are two of the three units vacant? 

In LA you can add ADUs so many investors buy properties with alleys or on a corner lot and build an ADU with 2-3 bedrooms and rent it out for good rent but then I think you are subject to rent control since then your property turns into multi-family and in LA there is rent control on multi-family (It might be harder to get insurance now a days for the ADU because of the current insurance crisis in California). 

If you can't keep control of your personal finances, you are highly unlikely to succeed in real estate investing.

My credit isn’t great either due to several factors (some beyond my control).

You have no control over these services.

Or, can I indicate that the house and an acre of land is part of the rental agreement, and the additional 5 acres is still in my control?

And I feel the ideal portfolio can benefit from the diversification of both.I feel directly owned properties are great because they give me maximum control and the ability to tweak them exactly how I want.

There are requirements in the middle here that have nothing to do with the estate and are controlled by the lender as @Lynn McGeein said.

It is certainly a possibility, but I wouldn't say it probably will happen.This depends on so many variables that are mostly controllable based on proper market research such as a quality property in a great location with great amenities.

This would be much worse for buyers and sellers as they'll have less control and less transparency.