Congratulations on the arrival of your "new baby" André! I think that you will find the lens/camera combination to be an excellent performer.
The Pentacon prisms are indeed very dim. They can be replaced with the much brighter Kiev prisms if you desire. Rolf Dieter Baier makes a Kiev prism
adapter for the Pentacons (I use one on my 6TL and recommend it - but it is more expensive than what you paid for your camera). See: http://www.baierfoto.de/
The in-camera focusing screen can be be replaced with a much brighter screen and this also helps.
Rolf Dieter Baier also has published a film winding procedure which will help prevent frame overlapping (not your problem, but ....?). The URL is: http://www.baierfoto.de/transportengl.html