No money crypto, baseball cards, stamps, coins, skateboards, bikes. 

If I dumped all my cash into this (I also have stocks and crypto etc, so I am diversified) I could in theory generate enough income to reach my goal, however I am nervous that buying in a different metro may have been a much better option, or buying C grade SFRs and duplexes in a peaky market will comeback to ruin me, or buying apartment buildings / complexes would have been a much better option.Also if I want to buy apartments, how do I accomplish that?

You will be locked in at a much lower fixed rate and you'll knock out that debt using cheaper dollars over time as inflation erodes the value of our currency.

I currently have no real savings outside of my company's 401(K) and only a small amount of liquid stocks and cryptocurrency that I could sell.One of the private equity firms founders suggested flipping a couple multi-family or single-family homes in order to pay off my debts and build a war chest to be used as a down payment on a rental property (I thought this sounds like a good idea). 

From the history (real estate, stock, crypto currency) don’t end bad until it reach the super super crazy stage.

Looking to get a rental or two with my current cash pile, I do not believe in a direction at this point in stocks, crypto, or most commodities, so I am not trading them.

In which currency will I have to pay?

A US real estate crash is still small potatoes compared to the currency instability in much of the rest of the world. 

Flips, buy & hold, crypto?

When I did this myself, I only had 2-5 tenants near enough the currency exchange to take advantage of this.