If you happen to have an older version of the SDK just download the new one from the Sailfish OS website and follow attentively the instructions (it will detect that there is an older version already installed). The user has 2 options: either to remove the old version (there are instructions presented by the installer on how to do this) or to update (I don't know personally if it will update from qt 4.x to qt 5.x ... so I just removed the old one and clean installed the new version).

Here is another tutorial:

Sailfish Tutorial

For beginners in Qt, have a look here: http://qt-project.org/doc/

Another tutorial on Qt: http://quitcoding.com/download/Qt_Quick_Game_Programming_1_0.pdf

(Timo, i think the 2 last posts point to the same tutorial)

For a bit more discussions and maybe even a place where to ask specific questions: https://lists.sailfishos.org/cgi-bin/mailman/listinfo/devel

From @JolaHQ: "For developer related questons you may also turn to [email protected]."

"Developing with SailfishOS - a short introduction. by Sven Putze"
http://hardcodes.de/SailfishOS/Developing-with-SailfishOS.pdf

I have not heard anything about that so far. Try asking jolla directly or pose that question on the devel mailing listt.