ph3 cars got rear discs, so that will be an 04 plate onwords and a few late 53 plates. if its got the ph3 interior and front end it will have rear discs, not that they are much of an advantage as they just cost you in snapped handbrake cables and groaning rear bearings that the cars with drums dont seem to be so bad for.
initiale was the highest spec model, dynamique was the most popular one to go for as it was part of the sport range and had all the nice toys, extreme 4 models were similar specc'ed to the dynamique but a bit less toys.
loads out there have the digital climate control with electric sunroof it was a £500 option so look out for that, if you look about then a few got the xenon headlights option and you also find them with uprated cabasse stereo and 6 disc changer.
mpg is pretty pants on them, my ex mrs had one and it wouldnt do anymore than 35mpg with her driving it like a granny, she used to average 60mpg+ in my dci100