yes
yes it can
To enable your Pokemon to learn Frenzy Plant, you must visit the Move Tutor on Route 228. Obviously you must have obtained the National Pokedex. Note that only Venusaur, Maganium, Sceptile and Torterra can learn Frenzy Plant. As for Pokemon Diamond cheats, I do not have any.
He doesn't learn it by level, a person teaches it to starters (stage 3). you go to the place with the villa then you go up till you see a house. Note: The Pokemon must be attached to you (like you).
on route 228 there is a house talk to a man he let torterra learn frenzy plant ,same 4 infernape but he learn blast burn again with empoleon i think he learn hydro pump
Tortera learns leaf storm at level 57. I would recommend not evolving it because grotle learns i at level 52. And turtwig learns it at level 45 so you should wait to evolve it.
Tortera because is the only starter Pokemon that can learn earthquake witch is powerful.
In Pokemon Diamond and Pearl you will have to go to route 228 and talk to an old man, I think you might have to do the same in Platinum.
You can't teach a Roselia Solarbeam without using a TM and only finally evolved starter grass Pokemon can learn Frenzy Plant.
The Move Tutor in a building on Route 228 will teach Torterra Frenzy Plant. (If you are playing Diamond or Pearl, that is.)
Kadabra will learn it not sure when.
Level 32.
No, not all Pokemon in Diamond can learn Hyper Beam.