They use deposit slips and drop the rent off at the bank.  

I'm trying to wrap my head around working with investment capital long term, and there's also the potential for some seller financing from the building owners, and my cousin is on the board of a bank which could also come into play.

No bank involved just yet.

The deal worked out okay but the agent my borrower worked with wouldn't release the keys, even after escrow closed, until his commission hit his bank account, that among other small issues. 

You are WAY too eager to leave your job for investing when investing takes years to deliver a return comparable to your job unless you have a bank vault of money to play with.

International buyers and investors bring with them additional privacy concerns, particularly around how their data is handled when it crosses jurisdictions.

I'll pass that along to my clients...........with Infinite Banking policies.

Banks won’t loan money to purchase land (usually); so any buyers will either have to be flush with cash up front (which severely limits your buyers pool) OR the seller has to make it easy for an interested party to purchase the land.Seller-financing works great with land, as do land contracts.

We sent 6 offers, one per week until the bank finally accepted.How did you finance this deal?

Some of what they are saying is correct, like having a separate bank account to hold security.