With remapped ST's and clutches some maps I found did give the clutch a harder time, others didn't. Example with my first ST, Dreamscience DSCI would make the clutch slip quite easily, though I admit this was partly down to me as they didn't recommend running it with a big bore downpipe, intercooler etc as these let the boost go higher than on a standard car. Changing to Mod B or Bluefin stage 3+ etc it was fine.
Even then it wasn't full-blown clutch slipping like mad, you'd just see the revs rise, drop and rise again ever so slightly around the 3k rpm mark if accelerating in a higher gear. I saw the same in a Mountune mapped ST, which caused a little bit of a stir at the time as they'd claimed the clutch would never slip on an MT260 car....the owner of the car had never noticed it and he left it as it was with no issues.
Going to Collins stage 2 with my facelift ST you would get the same now and then, must have run the car for 2 or 2 further years before I decided to get the RS clutch fitted and even then the old clutch wasn't in that bad condition once it was looked at.
With 100 cell sports cat my engine light stays off, in some very rare cases it would come on during colder weather and if car was driven really gingerly for several days (like during heavy snow) you'd get a cat sensor dtc but easily cleared with a code reader or pulling the KAM fuse, though I'd say it's always better checking what the error code is first.
Mpg-wise I'm generally hitting 25-27 with day to day running though I've never checked the accuracy against miles vs fuel put in the tank. Once or twice I've been caught out going on 'enthusiastic' drives with say 60 miles to go showing and the fuel light popping on a little bit earlier than expected. Resulting in 7 miles driven with 0 miles to go on the dash
I would have taken one out for a good blast to see what it's like first