The dynamique spec had manual air conditioning as standard - unless the "comfort pack" was specified as an option. This gave you climate control and a sunroof. Not sure about cruise tho, think that came with 2004 models. There was a minor facelift to Lagunas in March 2004, If you have a 2004 model you should also have rain sensitive wipers ( but not auto lights).If you haven't then chances are it is a 2003 model. Our lag was also registered June 2004 and IS a 2004 model as it has latest seat trim/dash material & "auto lights". It was built in Feb2004 as far as I can tell as various stickers on under seat wiring,under bonnet etc have dates of feb2004 on.
If you have got full Renault warranty then don't bother with another aftermarket one. The Renault warranty will be ok.
There were issues with 1.9dci engines in particular, with less faults reported on the 2.2dci. It basically came down to 18k being too long inbetween services.
Use fully synthetic
(5w40) every 9000 miles and you shouldn't have too many problems.
A lot of the problems with the Laguna II were also with earlier models ( 2001/2002) and issues with tyre pressure sensors and turbosin particular seem to have been ironed out.
You have made a good decision, just enjoy your car. All cars, no matter what make or model will go wrong at some point. Try not to worry about it, enjoy your new car, knowing you have a warranty as peace of mind!