I have the konigsports and used to switch between hardest and softest settings depending on whether I was driving to work or enjoying the weekend. Ive found that the hardest setting 'softens' up a bit anyway and wasnt to hard to start with.
They are holes used for letting water out of the inside of the car (as I found out!). Shouldnt fail the MOT on them at all unless the are rotting away around the edges I suppose.
I believe Top Gear did a test and Optimax came out on top in terms of providing more bhp. Ive tried both and tbh I couldnt tell much difference but Optimax may have more additives in it to keep the engine clean, but im not sure.
I think the banjo clip is the way the hose connects to the back of the caliper. The spacers that are made by the guy on the corrado forum are basically thick washers but are fine for the job. Both the longer bolts and thicker washers are needed whether you have a late car or not.