Hi Simon
Your new classic is a very nice B&O product. I think you will look into 3 main critical areas.
The Beomaster - it is important for your use and sound of this to see if a stereodecoder is inserted. Then the more ordinary points like lamps and functions switch cleaning is recommended. All this of course if the set is fúnctioning :). Of course I would strongly recommend a full restoration.
The Beogram - I am sorry to say a lot of the Beogram 1000 suffers from a motor problem. Som times this can be solved by a restoration of the motor, but not always. But - the positive point here is a aother Beogram 1000 is very cheap and you can easily replace a faulty Beogram 1000.
To your question - the arm ob all Beogram 1000 is a ST/L 15 and you can use also the SP12. SP12 is an excelent cartridge and actually one of the best of this SP series. You can find all info you need here on Beoworld. At the time of release this was the most expensive.
The speakers - to really obtain the best perdormance of your new classic, pay atteention to your speakers. I would take them out and clean them and after that I would coat the cones. Hopefully this is enough. If you hear distortion you might need replacement speakers og repair of the speakers.
Clean your connectors carefully (all of them)
Ude a good antenna for the FM
And - the most important - enjoy your true classic B&O
/Frede
Beolab 5000 - "If another amplifier sounds different then it needs repair!"