I installed a Pioneer X1R nav system with Audio/Video capabilities on a 2005 Laguna (check on the How To section, will post some pics this weekend). Screen is 6.5" if IRC.
The screen slides out and remembers the previous position, plus it's possible to change angle anytime. In your car model you might have a problem with the cover lid limiting your screen angle.
For now mine sits on top of the stock radio just in front of the vents, with all the possible problems SportTourer refers to , air conditioning in summer being especially bad for these screens. Best way to deal with it is closing the vents or try to swap the stock radio (will do this weekend).
In a 2002 Laguna though the vents will be much higher than your screen so the problem should be minimized. Please check the link
And yes for the stalk control you'd better check with various manufacturer (Incartec for example). I would go for Alpine or Kenwood, there are quite a few adapters already on the market.