And 3 English boxes will net you, on average, 33 holos, 3 Lv.X and 72 rares, and exactly 324 uncommons, 540 commons, and 108 reverse holos.
Despite some people saying that not every box has a Lv.X (and I do believe them, of course), every single box of DP-on I've ever opened has had exactly 1 Lv.X in it. So I would say a very large majority of boxes has 1 Lv.X.
There is. But you only get 20 packs in a JPN box. So that's 3 x 20 = 60. Actually, it'd be 51, since I think the lv.Xs count as foils. But still, 51 GUARANTEED foils is better than 36 (on average) foils from an american box.