Chase Bank does ACH collections, but they charge for it as well. 

Glad it's going well for you!

Like everywhere else, investing is first and foremost about numbers.While you generally don't run the regulatory risk like you would in the US, Mexico City might be the exception and I would stay away.Tulum is being completely overbuilt so I'm not sure how you could be profitable long term there.Merida doesn't have all year-round mass tourism buy maybe focusing on a niche could work.Puerto Vallarta is great but it's become much pricier lately so you might need to find a deal if you want a decent return.Hope this helps!

Could set him up with Cozy too but Venmo is easy and works well.

Any tips on platforms or techniques that work well?

Doing that will eliminate part of the hassle but I assume you're aware that you will likely make much less money than with US LTRs and that the laws are much more tenant friendly than anywhere in the US.I know Valencia quite well with the perspective of a North American (and European) as I was going to invest in STRs there after the Costa del Sol but, sadly, they've banned STRs there so I had to reconsider.

Zillow and Facebook groups as well as insurance placement companies can be lucrative as well

If your COC doesn’t exceed 10% and you expect zero appreciation you’re taking too much risk for a little more return. 

Other than California, which I can't afford right now, the places I've been looking at and can afford...well, I don't know anyone in that area.

I wish you well in your investment journey.