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

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.

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 am assuming this needs to be relocated outside the unit and also I need to add moisture barrier to the foundation/floor etc.It's my understanding that a regular designer cannot help with this and I will have to engage a specialist to help with this.

That said, I focus on a very different market segment (mostly 800k to 1.5 mm on the residential side) so that dictates how I approach things.Water issues are the number one cause of litigation in my line of work so I am very focused on water/moisture management. 

Is this a normal thing with moisture trapped under the laminate padding?

They can look for recent damage and do moisture tests.  

In addition to new vents we are also considering installing cedar planks on all three bathroom ceilings because it’s mold resistant and (hopefully) handles moisture better than paint.Does anyone have experience with this?

A whole property humidifier requires maintenance, is prone to repairs and increases risk of mold through higher levels of moisture.

Additionally, there is evidence at a number of windows of moisture penetration.