Just got an AA S220 Target foresight, and an SMK diopter for my HW30S. The idea is to have a good Bell target set up if I ever have the opportunity to do it, and also just to have a low powered but accurate baby springer for short-range but accurate plinking.
With that in mind I was originally set up for a combination that seemed quite popular on here: a williams rear peep sight and the fibre-optic HW front sight. Sadly though, if you saw my moany thread last week, Herman W buggered this right up for me by pressing the barrel dovetails off-centre, so with some help from a few members I have gone to plan B - new foresight, new rearsight.
The foresight was straightforward to fit with a little filing of the dovetails (no compunction about doing this as they are off-centre and thus useless, and being misaligned would have made filing grooves in the AA foresight unnecessarily complicated). I bought the SMK diopter a) because it was cheap and b) because it had a lot more area on the dovetail clamp compared to the AA/Daisy rear dipoter. TBH it seems robust enough and reasonably well made.

I have no clue whatsoever about diopters though, so a few Q's;

Where can I get elements for the AA foresight? Are they compatible with another brand?
Is there even much advantage to messing around with elements?
What sort of eye-relief should I have on the rearsight?
What should my sight picture look like?
How much space should there be between the rearsight hole and the outer ring of the foresight?

What else should I know about using these kind of sights?