Servicing really depends on how much money you wish to spend on it and the condition of the current engine. If you are happy with it then just a normal service will do.
100K service i would replace the cambelt, oil and water pump and all the seals (oil pump, cam seals as a minimum.
IF YOU WANT --> To spend even more money
If you are looking at doing your head gasket then i would suggest going all the way.. doing a full strip down, measure and put back together with new main / big end bearings and rings. Have the bore checked etc