My biggest concern and highest priority would be climate and humidity control. We don't want condensation forming and making rust on our dies, tools and rifles. We don't want the humidity too high or it will also eventually affect primers and powder. I've heard that high temps will also affect powder eventually by drying it out.?
My other priority would be security, and making sure the garage doors are able to be locked down really good.
Elaborate benches are nice, but not necessary. I do all my loading (have for years now) on an old pine desk and kitchen table. But, if money and space aren't a concern; build the best bench you can, maybe put a shelf or two below the bench top and install some cabinets on the wall above the bench top. I'd put lighting under the cabinets to light the bench really good. Be sure to plumb in power receptacles for all the electric reloading tools that might someday fill the bench, like tumblers and case trimmers and powder dispensers and the sky's the limit these days. I'd also make a separate bench area for cleaning guns, mounting scopes and such.
Sounds like a cool project, best of luck with it.