The owner's manual will have a maintenance schedule inside.
It is never a bad idea to swap out all the fluids on a new/used vehicle as then you know where everything is, what oil belongs in what component and how long it has been in there.
Drive belts are generally only changed when they show excessive cracking, unless you want to fit a new one and save the good, used belt for an emergency spare.
A basic rule of thumb for engine oil is change it every 3 months or 5000km, whatever comes first. Use a good quality oil. While you are under the vehicle give everything a good coat of looking at to avoid nasty surprises and keep an eye on the brakes.
Hope this helps.
"Your only supposed to blow the BLOODY DOORS OFF" Charlie Croaker. The Italian Job. 1969.