Does BM have private/public methods like C#
No.
and overloading too?
No.
Is it worth buying MAXGUI?
If you want to create Apps, certainly. If you want to create games, probably not.
Can you make small programs such as a simple chat proggy that stay in systray but loads most of its data when you're using it (that make sense? LOL)
Yes. There's one on the first page of the gallery right now.