That's an interesting idea...certain moves could be used at the same time to combine other moves, which could maybe be a way of teaching Pokemon certain moves. This wouldn't have to apply to all moves, of course, but...that's actually a really cool way of looking at it and can kind of fit in with Contests.
That's a great idea as well: type advantages in specific terrains. Yet maybe for Pokemon that aren't necessarily of that specific type, but know a move of the type, can get the advantage as well. (ie. Linoone using Surf gets a 10% boost on it's attack). But let's get a good list here:
Normal: Doesn't get any
Grass: Plains (most grassy routes)
Fire/Dragon: Volcanoes or any generally heated or humid place
Water: Lakes, seas, anywhere underwater, and when it's raining?
Electric/Steel: Laboratories and Plants?
Ice: Snowy areas and icy caves
Fighting: General buildings?
Ground/Rock/Steel: Caves and mountains
Flying/Dragon/Fairy(?): Skies or otherwise elevated areas
Psychic: No clue
Dark/Ghost: Any time during the night (assuming there's a time system) and/or in areas requiring flash?