Buy a gently used set for half the price of a new one, maybe much less.

On a walk-thru as a buyer, main thing I tell people to look for is moisture invasion since that can be expensive and needs to be fixed sooner rather than later. 

@Nicholas Daniels so, putting this gently, in pretty much any field of endeavor the question " Can I make a lot of money without doing any work?"

Foundation - cracks, moisture in basement/crawlspaceThere are plenty of smaller items but if you're getting into BRRRRs, these are the four major ones that could make or break a deal.

There is a moisture barrier between the two layers.Question #1 - Is it typical for there to be two layers of the subfloor or am I describing it wrong?

The only thing I can confidently say on the subject, is that, as far as replacing pool equipment , maybe I can shoot you a price that would help out with the financial impact, There are various pieces of gently used(some new) pool related parts/equipment here on hand, being as we operate a pool cleaning/repair business.

For example: was it caused by poor grading/drainage, tree roots, post-tension cable failure, water leak, poor moisture management (i.e. no sprinkler)? 

Your worst enemy here is moisture, so yes make sure your HVAC system is working properly and make it clear to the tenant that they notify you of any dramatic changes to the floor or noticeable water damage.

It is important for me that the whole system is checked properly, and I can be sure there will be no surprises like leaking valves or moisture in the basement.

I think if the city guy came by, he'd go nuts and the local foundation guy knows the rule.If the building is just resting on dirt w/o moisture barrier, mucho problemas.