Joe,
Welcome to BP!
I am not quite at the "retired Navy" stage (less than 5 years to go). I am stationed/live in SD and currently exploring all my options for getting into a local multi family property.
My restrictions are - I plan to owner occupy (I have a Wife and 2 kids) and need something that fits my family. Additionally, I will be working at Camp Pendleton so commute is a restriction.
I looked into FHA options however with limited down payments and short potential time on station in SD (2 yrs) I just cant see the math working as I would end up very cash flow negative.
I am currently searching for a duplex with VA financing in the $700-750K range. ( with certain assumptions regarding rents )
Depending on your plan for your current fourplex you may have some options - equity available?
Through multi-family searching I have seen a few deals that might work with a 50/50 partnership which allows more of a conventional down payment. I will PM you in case you are interested.
I have a goal of attending at least one REI meeting monthly - I suggest starting with some meet ups - you may find many options you would have never thought of.
If you are looking for an agent I could put you in touch with the folks I am working with - they have a specific agent working with a focus in Multi.
Cheers,
Mike