First time BMW owner checking in! 2008 X3 20K miles CPO.

Should I just simply rely on the car to notify me when it needs to be scheduled (as the dealer informed us) or is it better to be proactive and follow a better & more rigorous maintenance schedule? Where could I obtain a service schedule? I'm thinking about purchasing a service manual (just b/c I like to have these things on hand, not necessarily b/c I'd be willing/able to do the work myself). I see that I can obtain a service manual on Ebay (on DVD) for around $15. Is this a worthwhile investment? I just hate the idea of relying on a light to come on in order to know when it's time to service my vehicle.

Thanks in advance!