Houston would take some getting used to climatewise...you should visit in summer as it is very humid and hot and summer is long.

The Midwest humidity chills to the bone.

I would think that Houston would be perfect for a heat pump in winter.The bigger question, in my opinion, is how does the heat pump perform in our hot, humid summers.

Pics of both sides of the wall may help evaluate.For what it may be worth:Rising water typically is ground water or flooding.Condensation has to do with the difference of temperature on opposing sides of the wall along with humidity levels (layman's definition for sure...)Penetration has to do with leaks and differences in pressure on each side of the wall (i.e., strong winds)Multiple potential culprits.  

If it's too small then it will not keep up on the hot days,  but if it's too big then it will cool the house off too quickly, leaving it still humid.   

I have a plan of attack to deal with the issue, but I'm looking for a specific tool that you all would recommend to measure moisture/humidity in the crawlspace? 

For about $12, you could try these humidity test strips.

Here in the east, with heat waves and humidity, it is common for most air conditioners to cool down between 10-20 degrees below the ambient air outside.

You want to keep the humidity under 40%. 

That kind of humidity in an enclosed space is the perfect recipe for growing mold.