What seals would suit the Torterra

As near as I can determine, there are no other differences. If you don't catch Giratina in the distortion world, you can still catch it in Turnback cave later.

Simply anything but Chatter and Struggle as Bulbapedia states. You also can't Sketch Sketch I think. Struggle isn't really intended to be a "move", and Chatter is a Chatot exclusive, and highly unusual, move.

Chatter is the one of only three moves that cannot be Sketched, presumably because as a field move, if used by a Pokémon other than Chatot, it does not temporarily change the battle cry of the respective Pokémon to the recorded version even if audio is recorded. This is because recording audio via Chatter activates a Pokémon's alternative cry, where Chatot's alternative cry exclusively depends on what was recorded when the Chatter field move is used; however, Chatter still remains not Sketchable even in Generation VI, where vocals cannot be recorded.