What Dave ^ says.
Aside of the timing chain which should be good for the cars "life" read that as 150k - 175k miles, I'm not sure of the water pump. Seen a few posts from owners with upwards of 150k-200k miles on Cee'd/i30 forums and original chains and no mention of water pump.
If water pump driven off the aux belt (not sure) replacement may be easier. Maybe a cursory annual check for leaks at service time if you ask.
Glow plugs, only investigate if winter starting is taking longer and longer. I "double cycle" the ignition makes for a smoother winter start.
I also believe that the newer U2 CRDI has no dual mass flywheel, though clutches do not last forever contrary to what others say. My old 07 Corolla was needing replacement at 160k when I got rid at that point.
If anything, pay for a full underbody clean and rust proof? Attend to any bodywork defects that may turn to rust. Keep brakes in good condition - rust is the issue at that age.
Don't forget a failed DRL repair/replacement could cost you £200-300 a full dealer price, these are the costs that I'm considering.