Gavin, what are you trying to achieve? Looks or handling?
if just looks, depending on what ser 33 you get and what struts are on it, you can fit the lower spring pan and bearing (metal) from a sud, which is deeper and allows the spring to sit lower using standard springs.
If for handling I would get shocks, the springs, then bushes.
If you want to go mental low i got a drop of 60mm front by using lowered springs and sud spring pans and 80mm rear. At the rear there is a few different types of top rubbers, the thinner allows the rear to go lower. You will need to look at front camber as well when going this low.
The ser 3 set up are lower by default and adjusted for camber and should go on with no mods but they have weaker plastic FAG bearings, which are bad enough with standard setup let alone uprated springs shocks and bushes.
As mentioned before, if you are going seriously low you need to get the shocks short stroked to match, as I did with my set up, the handling was mental, ask pat lol
Good luck with the decision.