Items that require attention should be listed in the service book. Just follow that as a guide and work yourself through the list.
Most important would be engine oil and filter change, renew gearbox fluid and diff fluid. Brake fluid change would be advisable even if it is not in the list. Visual check of brake pads and rear handbrake shoes replacing any that are close to minimum thickness. Check out the discs for condition and thickness, if approaching minimum thickness maybe time to replace with new pads and discs all round. Check all flexi brake hoses and all runs of brake pipes for condition. Any that are very rusty should be replaced. Check all the tyres whilst you have the wheels off.
Plugging in a code reader will not tell you what needs doing it will only tell you if there are any faults and point you in the direction of the fault but beware just because a code is set it could be caused by something else being wrong up stream or downstream of the sensor setting the code. Air leaks in the system quite often cause unrelated sensors to set codes because they are receiving wrong information caused by unmetered air getting into the system.
As to the service book stamp, not really worth it given the age of the car, just fill it in yourself backed up by receipts for the parts and consumables used.
