Martin,
Yes the leanout can be shared between the bike & the sidecar or just the bike,the more leanout you have makes the steering easier.
The gearing depends on the load to be carried & if a 500 or 600cc engines are used & the load to be carried & what hills are likely.
I used 19 or 20 tooth sprockets on both types of engines,a 17 is far to low for nomal use.
Good Luck
POTTY.
