We pay a shade over $5000 for a 2 ton

The nice thing for you with a 1031 from that STR to an area like this is that you'll lose a lot of monthly expenses that LTRs usually pay. 

I am likely going to be paying approx 300K stupid tax on their account.

The seller will be responsible for paying the agent commission.

They know we will have more business for them, and we always pay when the bill arrives by hand.Brochure process- you can google Self Storage and pull up a brochure for a location for sale. 

The 600k is rolled into the Y2 build (same as above), this is repeated for 5 years at which point the Y1 build is refi (will have approx. 120k in equity build just from mortgage pay down, no apppreciation factored in.

A like-for-like property in Mexico is much generally cheaper than in the US but properties in great locations aren't that cheap that you can pay cash for 4 properties with $400k (unless they're minuscule) but you could use financing if you have access to it.8.

It has not been smooth at all as most tenants do not want to pay.

Treasury bills are paying 5% and if you stagger their maturity you could have the money ready to go if you find a better opportunity.

Paying off $100K on a loan of 6.75% is the same as investing $100K in an investment that returns a guaranteed 6.75%.