Thanks for everyone's comments!
ben_gsr2s: Yup I had quite a bit of problem with the Castrol Celica's decals as they are quite hard / brittle, so I need to use a lot of decal softener to allow the decals to conform to the curvaceous surfaces. Some of the most problematic areas are the roof, the two vents on the side of the hood and the side mouldings of the two doors.
As for the panel lines, I used Tamiya's enamel paint (german gray on the 92 model, sky gray on the 93 model) thinned with enamel thinner.