Yes, that's right. Lemons are more sour than oranges, but they give the meat a lot of flavor due to their acidic qualities.

If you're going to marinate it, then a ziplock bag would do just fine... unless you don't have any. A bowl or pan would do just as well, I suppose. Gojyo always did like the garlic best.

Mind you, I've never actually cooked shark before, so this is just a guess. It shouldn't be too different from most fish... hopefully.