Richard,
Absolutely okay to ask questions - that's what the forums are for, among other things!
I bought my suspension bushes from Bristol Cars Services (Brian Marelli), and unfortunately I didn't record dimensions before I installed them.
I did however document a fair bit of my experience with my own 411 S5 front suspension, which will be almost (if not completely) identical to your S3 -
see this thread
Re the veneer, if is it just the varnish that has deteriorated and the veneer is okay, be very careful when sanding - the veneer is thin and very easy to sand through. Then you will definitely need to replace it!
My personal view is that trying to match veneer is a waste of time, because new veneer will darken over time. So if you replace it you may as well do the lot. The dash panels are flat, so should be easier than the side trim.
The headlining in my 411 S5 is grey vinyl as well, and I don't have a sunroof. Although I think the headlining in two of the Astons I have owned was also vinyl ... Anyway, Bristols cost a lot more than Astons so there's no excuse
