-Use it to invest in some sort of 'side investment' to supplement my retirement.

Most of the numbers are driven off of generic percentages; 20% down payment, 20% of purchase price for rehab, 5% for closing costs, 6% for vacancy, and 50% for operating expenses.

(ie. seller pays this or buyer pays this as spelled out in the generic contract might be exactly opposite of what you and the seller agree to.)With all of this said, it is wise and realistic to write in contingencies that allow you time to do your due diligence.  

I am looking for a way to supplement our income for all the lovely things that life throws at you.

Quote from @Pedro Hernandez: That's a very generic question.

I own some acreage that I cash rent for grain and also have a tiny home on it to supplement rental income.

@Austin Janiszewski if your current primary (Property A) is renovated and will generate positive cash flow after renting, consider this scenario:Instead of selling, utilize Property A as a source of supplemental income to offset the higher interest rate environment.

Without supplemental income you want to be more conservative, but with supplemental income you can stretch these a bit

They planned to buy a large apartment house and operate it through a property manager, providing them a nice cash flow to supplement their other retirement income.

You would have a property that would be doing something for you beyond supplementing your new jumbo loan.Last thing I'll say is this.