Your clutch should be fine. Not many people complain of slipping clutches on a GTI - mostly on ED30's. I can only recall two people that have mentioned clutch slip on a GTI. If you treat it properly then it will be fine.
Spark plugs? Heard nothing about that. When remapped it is recommended that you change them earlier than the VW Service regime recommends, thats all!!
Coil packs - thats a known problem with many different cars. I don't think its especially re-map related though. I understand that there have been a few revisions of the coil packs for the Golf from the early models, so you can get the latest revision if you're worried about them.
Engine mounts - never heard of a 'busted' engine mount due to a remap. You may choose to uprate them, so that your car copes better with getting the increased power on the road.
I've had REVO stage 2 on my GTI since November 2008, and have not had a single problem. I would say that with GTI owners (not ED30) probably 95% on this forum have not had a remap related issue with their GTI.
The only thing you should really change is the DV, which if you go for a revision G VW part is only about £30!
It is said that VW alllow around a 40% headroom on their cars - as do their other German counterparts.
Do it, you won't regret it!!!