Pietje52 welcome to Flyertalk and to the QR forum. You will find the QR dashboard very useful in navigating through the forum for answers to questions, hints and useful facts.
Apart from the 32 kgs maximum imposed by IATA QR are usually flexible with checked baggage. Small excesses are usually ignored unless they are excessive.
Hand luggage will normally not be stopped unless it is excessive in either weight or volume. I have had my hand luggage checked at check-in twice in the last seven years. (once in Economy and once in Business). You should also be aware that some airports have their own rules which, they claim, supercede the airlines rules. Look at
http://www.flyertalk.com/forum/qatar...d-baggage.html for a more complete description.
Most questions about luggage are answered in the wiki on
http://www.flyertalk.com/forum/qatar...e-luggage.html thread together with the Wikis on the associated links.