As others have said, the belt on these should be done every 4yrs or 40k miles (60k km), so *should* have been done. Budget for getting it done if you cannot 100% guarantee it has been. In reality, the change schedule is to reduce the risk of failure to near zero, and even if not strictly followed, shouldn't be an issue. But given the reasonably cheap cost to do it (about 1hr labour and somewhere between €60 - €200 for the part depending on if you want genuine or pattern), its not worth debating further.
The Cambelt Kit is essentially the belt, 2 idlers and a tensioner. Don't just do the belt, its the idlers and tensioner that tend to fail.
Water pump doesn't necessarily need to be done. Personally, I'd check if the bearings were good, and no signs of weeping, and only change if necessary.
The aux belt tensioners tend to dry out their bearings, so a new pulley (less than €10) is alwasy handy to have on standby as well.
A plastic valve at the back, called the Heater Bypass Valve (HBV) tends to start to leak. I'd only replace it if it does leak. My last Omega is still on its original factory HBV 21years later. My previous Omegas had about 3 or 4 of them in my ownership.