An IRA would pay a small tax on such unrelated debt-financed income.

This helped my Debt to income a ton and I was able to close on the deal.

If the property can service the debt at 90% leverage between a senior 1st and the seller second, you're looking at a good investment!

Combine that with some government austerity and the debt issue improves.

Once we acquire the last 2 properties we will shift from acquisition to debt paydown.

More properties but more debt. 

For example, if your partner has income and no debt, perhaps you can invest through her, or if it makes sense to combine your income with her that might still get you below 50% DTI.

Most lenders will also look at debt coverage ratio which limits leverage at this time due to higher interest rates.

Or should I create a combination of all three?

If the answer is yes, then it's a no brainer to make minimum payments on your 2.8% interest rate mortgage, and use the funds that you would have paid extra to pay it down faster, to either invest in more real estate, the market, or anywhere else where you can get a ROI > 2.8%.If the answer is no, then feel free to aggressively pay it down as fast as possible, to become debt-free faster, and just have a large amount of money in savings or to splurge with.The bottom line is that your 2.8% mortgage is GOOD debt.