Very natty, and a lot of cool details. Going for some sprezz with the top button of the vest left undone? I guess that is cool, but I always feel it is an insult to the hardworking tailor who worked hard to put the button there.
Generally I would tell a guy to go with purchasing a grey three-piece instead of renting a grey "tux." At least one can get some use out of it post-wedding. I would suggest going with some details that would take it beyond a business suit: Peak lapels, a ticket pocket...and as someone else mentioned a lower-cut vest. And French cuffs, or course!