I think the rate would be higher so I to compare ROI on 5% capital returned vs additional interest charges.

What do you think is the best strategy to employ my capital, ability and time here?

Cons: missing out on some cash flow, capital gains tax.I know this is kind of a long post with minimal information but how do you know when to keep or sell?

If you buy a new, or newly renovated property,  you may not see any capital expenses for the first several years.

The only thing we can bring to the table is capital.

For me to find capital for 20-25% DP would take me 2 years and I have set up a goal for myself to acquire the minimum of 4 properties before I am 40 years old.

As mentioned above, that doesn't leave you with much room for error in case any significant capital improvements are necessary. 

Or is it beneficial to pass it on in an estate, for the step up in basis, and then we sell without capital gains?

Presumably at some point, once you've built up enough equity through BRRR and made enough money through monthly cash flow, you would be able to get your initial capital out and yet keep "substantially all" of your assets in "qualified opportunity zone property" (90% for QOF and 70% for QOZB). 

New mortgage brokers often will not have the experience and not have built up a portfolio of lenders they know will close the deal and not re-trade mid deal.My capital markets brokers close hundreds of millions a year in loans.