As Rolebama points out, there is no room for compromise with the braking system, it's a bit late to find out the brakes are not working at their best when you really need them.
Brake fluid absorbs water. (it's hygroscopic)
In normal use the brakes get very hot, therefore the brake fluid gets hot, if the fluid has water in it this can turn to steam, steam (a gas) stops hydraulics working.
Suspension components have got lighter which makes them more easily damaged, suspension keeps the tyres aligned and on the road, so well worth having an experienced eye looking over them once a year.
Engine service is related to use or miles but it is complicated.
The oil is a package of chemicals, which deteriorate over time, the oily part will oxidise, the detergent gets spent (full of dirt), the buffer (neutralizes the acids from combustion) is used up.
Water from combustion and unburned fuel accumulate in the oil, with modern engines steps are taken to try and get the oil hot enough to boil them off but if the engine never gets hot enough then they affect the lubricity of the oil.
The oil filter, catches carbon from combustion and metal fragments worn off the moving parts.
If a engine was started and never stopped it could cover a very high mileage without attention, because it gets up to temperature and stays there.
An engine that doe's frequent stop starts (short journeys) suffers extra wear because each time it stops oil drains away from the lubricated surfaces, at next start lubrication will be marginal until the pump gets oil moving again, and the moving parts are designed to fit when the engine is at running temperature so when they are cool they are a bit loose.
From the above we can see that there could be two different mileage intervals for engine service, a high mileage car will probably go past a year but a low mileage (stop start) could be less, the compromise then is to say 1 per year for both.
Coolant, is usually water and antifreeze, the antifreeze also has rust inhibitor and I think most have a detergent, the rust inhibitor and detergent get used up over time but as water is added to the cooling system (topping up) the mixture gets diluted, at the annual service it should be checked and any overdilation corrected.
I think, green antifreeze has an overall life of 3 years and long life (orange or yellow) 5 years.
Should you have a car with waterless coolant the coolant has a life of 10 years' (NEVER TOP IT UP WITH WATER)
I hope that helps.
