Well rode almost 5000 kilometers on my carbon drive and it seems barely used. Many people report their belts first needed replacement at the 15000-20000km mark. The belt needs no maintenance. The only thing you have to keep an eye on is if it is tension correctly. and I would heavily advice you if you get a belt drive, buy the tool to measure the tension.
I would recommend Rohloff or pinion to get the ultimate experience.