I am interested in an investment where I would provide capital to ATM company for a return.

Unfortunately with those numbers it's tough to find a non-bank lender/financial institution that will lend.Usually loan minimums are $50K and the up to 75% LTV on purchase-money/70% LTV on cash-out refinancing, which basically means you need up 25-30% depending on the type of financing. 

Do you have a non-recourse loan?

What do you file for this "income overseas," do you file SChedule C self employed on your personal 1040 tax returns ?

Some agents might offer flexibility, like a non-exclusive agreement, especially if you’re upfront about your plans to explore multiple opportunities.

If you purchase with 20k you will be paying PMI and the returns are too low. 

My favorite was a hoarder house full of trash that took me six months to turn around, but it turned into a killer deal that earned me a 600% return.

To beat 5.25% mortgage rate....the corresponding, offsetting stock market return would be at least double that...To answer your question requires (1) knowing what risk adjusted return you will be able to earn in the future (2) knowing what interest rates will do in the future.  

Pros: pay off mortgage sooner, one account for everything (all cash + deposits + expenses are paid from the HELOC)Cons: higher interest expense, higher opportunity cost (putting all your cash into the HELOC means you aren't investing it into other things that could yield higher returns)

I plan to continue to invest in a mix of both RE syndication and our own rental properties going forward depending on what makes the most sense and offers the best returns.