Welcome to the forums
. Though, in case you're not aware, the discussion on these forums tends to not be very geared toward general game design discussion. It's usually more focused towards discussing SFML itself. Like, how to use it, what are some good practices, etc. Specifically, you may have more luck asking about Box2D and how to implement destructible terrain elsewhere. I'll try to give some basic answers to some of your questions though.
1. It is hard to give an answer without knowing how complex your collisions and physics need to be. If you just need to check collisions between, say, the player and a wall, Box2D seems like overkill. SFML provides a basic way to see if
one rectangle intersects with another. But, if you need your objects to do something like tumble through the air and collide in complex ways, then Box2D may be more appropriate.
2. I've never actually used it, but yes Box2D seems like a pretty popular choice when a game needs to incorporate advanced 2d physics.
3. Are you asking how to implement splitting your terrain into smaller squares, or if this is the best method to implement destructible terrain? I think splitting the terrain into smaller squares would be a fine start depending on your needs. You can then draw these squares with SFML's
vertex arrays. Once you have something in place you can see what you do and don't like about it and then perhaps you'll have more specific questions you can come back with.
4. Can you be more specific with what you mean by "transitions" and "views" or provide an example of the effect your going for? If you mean you want to do something like a blur effect when switching between your top-down level and side-scrolling level, you could perhaps use a
shader. I think there's an example of a pixelate shader that ships with the SFML sources. There was also someone on the forums recently that made
a library that might help with what you want (though, I've never tried it).
