You need AC. Where/how it's installed is not so important for managing humidity.

wall mounted?

You need to find you a "good" HVAC company. It's a matter of air balancing and the proper size unit. Home construction, insulation make a big difference as well.

steel building, closed cell foam insualtion - throughout, cross flow design, airtights passive so why do i need central air A/c? With crossflow and correct ventilation openings and protection from direct high sun on all the windows why is it necessary.

Have you lived in the area? No one mentioned central AC.

Good HVAC design depends on many things. As ljksen said -- find a GOOD company who is familiar with your type of building and will do manual J calcs to size the unit.

Lots of good info from the passive house crowd too.