I have a mini split a/c unit if my den. We have a large house and the den is a SW exposure at the far end of the a/c duct so cooling it in 100 degree summer was always a problem. The mini split works great. I'm not sure if they make one with heating, but my husband has a gas wall heater in the garage. It keeps one bay of the uninsulated garage warm in the winter. As far as the water goes, that can be a real problem. We've fought (or at least the DH has) water seeping into the garage for 15 years now. He finally lowered the back yard and made tiers so hopefully we won't have any more problems. I'd definitely go with the flooring that can be take out and dried and re-installed. It sounds like you might have a chronic problem. Also make sure your power strips are mounted high on the wall so they don't get wet. Wall mounting them makes it easier to plug and unplug your machines anyway.