So now, i am considering selling it and paying off the majority of my first rental (I owe about $255k so i could payoff a big chunk and pay off the rest with added payments over a year or two), or put the money into stocks and grow it from there.

Here are some steps and considerations:Lenders look at your debt-to-income ratio (DTI) to determine your ability to manage monthly payments on the money you borrow.

Also, important side note, property taxes here are super low generally, not only because the tax rate is low, but Idaho is also a non-disclosure state so the government doesn't get to use data to accurately assess your property and as long as you are wise enough to avoid telling them what you paid, your property will often be assessed far lower than the market value.

Typically investment properties requires 15%-25% down payment depending if it's a single family or multifamily.

But I’ve found ways to get the cash for down payments then have harvested equity to scale up. 

This is why I'm taking the route of a FHA loan since the flexibility on approval for self employed investors .Can I open an LLC to manage this 4 unit property ,so tenants can make payments to my LLC?

This is not a non-owner-occupied investment loan product.

There is also the thing of a physician loan where I wouldn't have to put a down payment on the house and secure a loan although I would want to try to aim for a fixed rate (or maybe variable since interest rates are potentially going to be cut in the future?) 

Would I assume liability for non payment?

I'm sure the numbers are more favorable if you completely own the property and don't have to do mortgage payments or have some other bond or something to cover the mortgage payment cost.