As above a Paint Thickness Gauge is an 'essential check' in case any repairs or previous work has been done.
I do admit I still work by eye and feel!
You should have a good 150 -200 um typically more suggests a repaint/repair and less well no space for errors.
A gentle full wet sand and machine polish process should remove around 5-10um against a clear cote of typically 50um.
If you have the 'peel' surface then its unlikely any real work has been done before.
A 1500 and 4000 wet sand and then a cut pad followed by a polish pad will deliver a reasonable finish.
It may be that a simple polish will improve the condition.
http://www.ttforum.co.uk/forum/viewtopic.php?f=31&t=945281
Took a few hours on this one.
Microfiber pads seem to work well on VAG paint used with Chemical Guys 36 and 38 compounds.
There are however tons of product options....
The aim is to improve not remove. Less is more... stop when it looks good.
Forget a DA as this will take forever. A rotary or ideally flex (even a big foot) will reduce time and effort.
Allow two days to do the whole car. Don't rush....
Detailing World has some good how too's.
If your near Winchester I can let you try some products....