Anything from horizontal to about 30 degrees downward will work fine. Just pick something that fits your aesthetic desires, and covers the cork with fluid
My father had a pretty large rack he used for his wine... they were horizontal and would fit 5x5 bottles per cube. I don't know the total number of cubes but it was large. I'd say 4 cubes high and possibly 8-10 long. Lots of wine, like 200 gallons if full!! I remember stealing bottles when I was a kid and getting tanked with my buddies on Merlot, LMFAO...