The ST sounds sweet with a nice cat-back fitted, but without causing annoyance for the general public as well.
DSCi isn't so bad with standard set-up, clutch wise but old memory coming back now seems to think if you've got uprated intercooler or downpipe then the boost levels can get too high and that's what the clutch doesn't like. Even then when I finally went for the RS clutch plus DMF etc last year, which seemed the ideal time for an LSD too
With AFR's I don't think you've got anything to worry about - with all of the most common maps I'm aware of, DS, BF, MT & Collins I've never heard of any problems in this area. In theory as the ECU takes feedback from 2 lambda sensors it's adjusting fuelling etc to achieve AFR targets, and unless something was specifically changed in the map this wouldn't be an issue. Can remember my last ST on a DS dyno day but running BF map that their probe in tailpipe said AFR was on low side, but Superchips's response was that by taking reading from tailpipe this causes an inherent delay in the measurement hence it'snot very accurate way to do it......