@Wjbender: Thanks a lot!

I don't wanna sound selfish but I'm starting to think that the renderer is capable of rendering some pretty nice scenes.
However, my artistic skills still need some work (actually quite a lot of work ._.)

And I FINALLY managed to fix the interface issue. The problem was that I'm setting up all the views before loading the level - which works just fine - but the parameters of the interface-view always got reset when loading the level (because it's position is not updated during gameplay) and it ended up somwhere, but not where I wanted it to be.

There are still some minor issues but fixing these will (hopefully) take less effort and cause not as much of a headache.