Keeping Size Down

So, I am looking to start making an iPhone/Android game. However I'm not sure the best way to do it, so I want to have like 100 puzzles in the game, its going to be 3D. I want to know the best way to do this though, each puzzle will use the same textures just a different model. So my question is this? How should I do it. E.G

Would it be possible/viable to make a new scene for each puzzle, or would it be best to do one scene then just load/unload the puzzles that aren't in use.

Also if I have 100 different models will that put the size up a lot? They are going to be very low polly. Would it be best to do modular parts and do it from there in the scene? This wouldn't allow me the customization I want though.

I've never done a mobile game and never had to worry about size.