The bike has 900 on it. The sidecar is to be installed by the dealer. I've taken the S/TEP classes that are offered here in WA and find it much easier to drive a rig than bike alone.
How difficult is it to replace the large sproket.
I've never replaced the sprocket on an RE, so I can't help you there. If anything I hope you're considering increasing the number of teeth on the rear sprocket (see RE #1's post), although I think it best for you to leave it stock initially.
Here's an indication of the frequency of maintenance:
According to the Owner's Manual, and with the following exceptions, each maintenance item should be addressed every 3000kms:
Inspect Inlet/exhaust valve seating: Every 15000kms
Decarbonize Cylinder head: Every 15000kms
Decarbonize exhaust system: Every 15000kms
Earth wire eyelet : every 12000kms
Steering Ball races: every 12000kms
Replace Gear Box Oil: every 9000kms (and check it every 1000kms)
Spoke tension: every 6000kms
Wheel rim run out: every 6000kms
Rear brake cams: every 6000kms
Hand levers and kick starter pivot: every 1000kms or earlier as needed
Check Fork Oil: every 1000kms or earlier as needed
Check front disc brake fluid level: every 1000kms or earlier as needed
Adjust rear brake play: every 1000kms or earlier as needed
Adjust clutch free play: every 1000kms or earlier as needed
Adjust decompressor cable play: every 1000kms or earlier as needed
See my RE Notes (signature) for one example of a maintenance regiman.
Matt