I do intend on holding them for a long time, but again this limits my flexibility in the short-to-medium term.Does anyone have any thoughts/suggestions for me?

Gets deeper from there, but that's the high-level.My goals included being work-optional well before the traditional retirement ages tied to retirement accounts, so therefore the places I put my money needed to afford more flexibility. 

This can lead to missed opportunities, especially when speed and flexibility are crucial.Personally, I’ve seen investors switch to creative or alternative financing options, like hard money loans, private lending, or even seller financing, to avoid some of these pitfalls.

With cash, you keep more of your return and maintain a simpler cost structure.Greater Flexibility: When you own a property outright, you’re not bound by monthly payments or lender-imposed deadlines.

2.Private Money Lender – I’ve heard they can be more flexible and might focus on the property value more than my employment status, but I know the interest rates are higher than conventional loans.

If there is no problem then the HELOC will provide more flexibility since the cash out re-fi may yield more proceeds after improvements when applying the 70 or 80% LTV limit whereas you might get improvement proceeds from an investment loan but you won't want to because there will be a lot of red tape, inspections, draws, lien waiver compliance and a lot of other crap they load onto improvement loans on investment property.

Their best bet is likely to sell on the open market...so why should they make less money (potentially) so you can make more?

In my area I'm allowed to rent it out that way but I don't plan to get separate addresses because I want to be able to have the flexibility to remove the doors I'm putting in should I ever want to sell it as a SFH in the future.

Your best bet is to contact the commercial banker at the bank who holds the first position mortgage on the property.

Key takeaways include being flexible and open-minded, using house hacking to build wealth, leveraging previous profits and equity wisely, seeing potential in properties with deferred maintenance, and patience and compounding efforts.