Speed is obviously a plus, but I am more concerned with it being able to handle the volume of read/write (as these Pi's will be up 24/7 and doing a fair amount of work). I had read the not all SD cards were designed to be used in the manner they are with the Pi's, and can become corrupt after an excessive amount of use. This is what I am trying to avoid. Am I being misled by that piece of information or are there cards better designed to be used at a high frequency?

I would like to use a Windows computer, however I have machines with all 3. I haven't looked into OpenVPN yet. Would having the Pi connect to the OpenVPN server on my home network allow me to control the Pi like I do locally with remote desktop?

You don't need a crossover cable to connect to your Pi directly. Simply set your Pi to have a static IP for eth0 and use remote desktop on anther PC to connect.