I would start ...with a good bar stool - to sit on ...for height...
3/4" plywood will flex way too much ..../ maybe if you double it up ...and reverse the orientation of one sheet vs the other ..it will be ok. A bench made up of 2 X 6's ...is better ../ with a good frame ...double up the 2 X 6's for legs...cover the top with some "hard board" or some kind of counter laminate...
For light ...a good Halogen desk lamp / with a adjustable neck ...like a drafting lamp works pretty well. There is no such thing as too much light. But you'll need decent overall light as well as the Halogen.
Think about the overall height of a metallic loader...especially if you put a case feeder on it at some point.
Check with your state or local fire codes on storing powder, primers ..and quantities that you may be restricted to.