rough idle and rattly chain means your chain is loose and possible timing is out
vxhall dealer should of told you there and then that the timing is most probably out and the rattle is down to your chain / tensioner
as for high idle it could be the knock sensor retarding the ignition due to the timing being out, could be your coolant temp sensor, could be your throttle body, could be an air leak but i would be more interested in the rattly chain and lumpy idle
I would ring up vxhall dealer and ask em if they checked timing whilst plugging a tech2 in as there is loads and loads of data about rattly chains especially on the Vectra B that came standard with faulty oil jet and chain components [providing it is original chain]
my advice is dont drive or start her up if you know the noises are coming from the chain area
good way of checking is put your hand on the top of the cam cover above the chain when you start her up and you will feel the chain slapping on the underneath of the cover
do a search on the forums !