Servicing, Servicing, Servicing.
An oil and filter on the 1.6's will come in at less than ÂŁ30 if you do it yourself using quality 5/30, you can get Quartz ECS or MC3 for about ÂŁ24 delivered, filters are usually around ÂŁ4-6.
Personally, I've always done mine at 6,000~ miles, same as my dads old C5 II 1.6 and as a result we've had no real major issues with the engines other than blowing seals which were resolved by using the slightly thicker ones.
His didn't have a DPF, but mine did and I had that removed.
Beyond that the EGR may occasionally need a spring clean if you have an hour to spare and are not afraid of a spanner.
My new C5 suggests that the interval is 20,000 miles, hell no! 10,000 tops!
Phil