The WPC core is a good product in moisture areas.

He also said moisture readings in some joists were in the 20-30% range. 

Basement has moisture issues that have to be handled correctly I would get an exhaust fan for the room and hopefully it has an working window. 

Basement - a couple of things 1- is not completely dry has humidifier that I turn on now and again to lower moisture as floors (concrete) can get some water in it. is this a problem for a rental?

We removed a large tree that towered over the roof causing a mess with falling debris on the roof and blocked all sun which left too much moisture.

With underlayment, people state what seems obvious -- that a thicker product will do a better job of deadening noise and perhaps of blocking moisture penetration through a concrete slab. 

i'm going to assume the blocks were filled with insulation which would take care of the moisture coming thru. 

Look into digging some soil and trench away from the house, put the proper foundation drains in, seal the foundation and be done.Having moisture in the basement continuously makes for a very muskey environment, I have hated that in every old house I have lived in.

All that hot air and moisture running through the pipe for years is bound to do some damage.

Anything from moisture to extreme heat to shifting ground to hurricanes to fires to harsh winters to EVERYTHING could happen when you invest in real estate.