According to the official website, 1st floor: 3,199 seats + 2nd, 3rd floor: 7,846 seats + standing: 480 seats + arena: 2,946 seats(max) = 14,471 seats.
But the capacity should be 8,000 ~ 13,000 as a concert venue.
1st Budokan show (May 2) was sold out, but you can get a ticket for 2nd Budokan show (May 3) through PIA (only a few tickets remaining.) 

John said "1st show and 2nd show in Tokyo will be totally defferent." in the Billboard JAPAN interview. (I'm not sure if he literally said "totally", but it says so in Japanese at least.) I wish I could go there....