Welcome Massirati!
I don't know the service intervalls for the F800, but I do know something about the F650CS Scarver! Belts!
BMW do not know how often I have to buy a new belt for my Scarver, but they say I have to see if it is OK every 10 000km. So I see if there is a loose tooth, and if it is as it was last time I looked - that is all!
I hear often the belt are going to snap if I get a small stone in it, but that is not thrue. Perhaps old type belt is like that, but there are metal cords inside the belt - it is not just rubber.
I have seen a stone go through the belt, and it did not snap.
And there is a man in USA, Dailyrider is his username, he rode 90 000 miles with his Scarver before he choosed to change the belt - some teeths was loose.
If you love to ride in snow/ice and in gravel/woods I guess a belted bike is not perfect. But don't be afraid of a few miles on a gravel road - I have ridden on gravel and I did not find a stone in the belt.
I guess stones/ice/twigs gives the pulleys for the belt a hard time, so it needs to be replaced more often then if there are no stone/ice/twig between the belt and pulleys. But I'll be suprised if those things make the belt snap.
The engine F650, Rotax, needs new oil every 10 000km.
The two cylinder engine on F800, with a wet clutch (like F650 Rotax); I guess it's about the same.
Tyre:
I had a Metzler ME Z4 for 15 000 km, rear, on my Scarver, riding alone all the time.
I'll get a new Metzeler Roadtech Z6 on Monday, and the salesman told me that one is as good as the Z4.
Bridgestone Battlax BT014R was worned out after 8320 km, but they told me it is because it is a soft tyre for fast riding - my pants get wet in 60m/h so I don't need that type of tyre, thank you!
I mentioned the tyre because I guess a heavy bike ''eat'' more rubber then my little one! And perhaps a chaned bike eat more too, because the belt makes the riding more smooth.
I didn't give you a proper answer, but I wanted to tell you I'm here, one of the few members here with a belted bike.
And I'm a girl, and I live in Norway, but who know if I'm OK after all?
Welcome, have fun!
And if you start a new thread in the ''I'm new here''-section we all get to know you a little better!

Liv.