starting C# 2D DirectX game

Hello. Im starting my first DirectX game. Should I write the ui using DirectDraw or Direct3D? I read somewhere that directdraw is or is to be depricated. I also wondered, which class should perform the collision detections, the engine, ui or moving objects itself. I dont have even a rough design at this point, this is so at the start. I never did a game with object oriented design, so the responsebilities of the classes are a bit fuzzy to me at this point... ps. Good design pointers are also accepted;) (and bad english is always my burden)