I'm not sure as I've never seen one with lows, but I'd personally go with the mediums to be safe, and I get a better cheek weld with mediums, but in all honesty, it's really just a personal opinion. The best option would be to measure to see what size rings you need.
As for your choice, you can put anything on it you want, but I wouldn't. The Burris Signature Zee rings would be a much better, choice and I'd stay away from the crappy windage adjustable bases on this gun.