So you can buy a four flat, live in one unit and rent the other three, but you have to live in one unit on the site. 

The properties are considered on a separate basis, you can actively participate in one and passively participate in others. 

Wife and I are both self-employed so acquiring a traditional mortgage is challenging based on our "on paper" income.

You can find tons of great deals on-market and off-market here!

My exit strategy is to refinance into a Longterm USDA loan, after the Tax Map Key is issued in 10-24months.I plan on farming crops on the land.

It takes a lot of phone calls and asking around, but you can normally find a local or regional bank that is willing to work with investors on these types of properties.Mike

Are there any other areas I should consider based on my budget and purpose?

I can open a HELOC on my residential property, but that may not cover all rehab expenses.

This can be a good strategy; I say this with one large caveat. 

Using a HELOC can provide you with the necessary capital at a lower interest rate to fund your next projects without leaning too heavily on hard money lenders, which can eat into your profits.Here are a some actors that you would want to consider:1.