re: Using Square to pay off non-CC accepting debts, earning rewards, etc.

Not quite, you're missing an important point. There is no "Square" account that holds money, the moment you swipe your card money gets sent directly to your bank account and Square takes a cut. So after you do the swipe, you owe $5000 on your CC and have $4862.50 ($5000 - 2.75%) in your bank account. There is nothing for you to get from Square, you have simply paid them $137.50 to get a cash advance.

This can be okay if you have a low CC rate, because now you write a check to your loan. If the loan rate is higher enough to cover the difference between the CC rate and the 2.75%, this is fine so long as you pay the CC back later before the rate expires. You're just paying a lower rate and paying Square a 2.75% fee to be able to.

Like I said in the other thread though, I think it's better to just charge normal living expenses on your card and pay the minimum. That way you aren't paying 2.75% to Square. And no matter what, always pay the minimum monthly balance on the due date, and be sure you have the whole thing paid off by the end of the teaser period.

Yes, this is some work which is why it probably isn't worth the effort unless you're talking about saving a grand or more.

ETA: I do have a Square and use it regularly.