If all you are looking for is cooling, you can put in window unit. You can even put it into the wall to the garage. It will heat up the garage, but keep the cave cool. I just had a company put in a heat pump to heat/cool my entire garage. Not the cheapest way, but VERY nice.
You can never have enough bench space or enough storage space. I would put in cabinets.
I covered my bench with matt white laminate. Keeps the area looking clean and bright, and you can see things on it.
Look at the height. My loading bench is higher than my work benches, so the presses re the right height when I am standing.
+1 for cabinets. Keeps the dust down on things, and adds a finished look. Little harder for those you don't want to know exactly what you have to see things you'd rather they not see.
Also, second the thought to build your benches to custom height. Really think through what height you want your presses, versus your prep tools, and build different heights to accommodate. You can also build to match standing height, and then get a bar stool of correct height to allow you to sit at the standing bench if you choose to.
Lights, lights, lights. Directional lights are really nice to point at your critical work areas, ie. where you have your scale or press.
Like the white laminate idea, also the stainless idea----laminate easier to work with and cheaper. I also like the idea of the poly'd board.
Might consider some form of pigeon-hole drawer set-up for your bullets, so you can remove a drawer to your work area and then replace in the set when done.
Would recommend against holes through the bench for cords--maybe another way to route them without places for stray primers or bullets to wander off. Yes, I know none of us ever lose those items, but if we were to lose hold of one, best not to have holes it can go into. I have high mounted outlets, and have my cords go straight up to ceiling and then over to outlet.
Room unit a/c is good idea. If you do it in an interior wall, be sure to remember to make a drain for the condensate to flow where you want it to. Otherwise, you will have a puddle on the floor, and might create a mold issue.
Good luck, and please post pics of construction and finished cave,
Tim