Alright, to start off, I have experience as an amateur Obj-C/Cocoa and Ruby w/Rails programmer. These are great, but they aren't really helpful for writing cross-platform applications (hopefully GNUStep will one day be complete enough for the first to be multi platform, but that day is not today).

C++, from what I can gather, is extremely powerful but also a huge, ugly behemoth that can take half a decade or more to master. I've also read that you can very easily not only shoot yourself in the foot, but blow your entire leg off with it since memory management is all manual. Obviously, this is all quite intimidating. Is it correct?

Python seems to provide most of the power of C++ and is much easier to pick up at the cost of speed. How big is this sacrifice? Is it meaningful or can it be ignored?

Which will have me writing fast, stable, highly reliable applications in a reasonable amount of time?

Also, is it better to use Qt for your UI or instead maintain separate, native front ends for each platform?

EDIT: For extra clarity, there are two types applications I want to write: one is an extremely friendly and convenient database frontend and the other, which no doubt will come much later on, is a 3D world editor.