Hi Jape,
The bolts falling off sounds like poor pre-delivery checks by the dealer.Upon buying my bike , I spent half an hour checking every nut and bolt on the machine, and nothing has ever come loose or fallen off, even after several 100klm off-road trips on rough fire trails.
Three batteries in 450klm? Did they die from lack of use, or is there a problem in the wiring and charging system?
With regard to suspension adjustments, the rear shock spring tension can be adjusted.I found that the best way to do this is to compress the spring a little by turning the adjusting ring and locking ring on the shock, then go for a ride over a predetermined course.Compress spring further, then ride over the same course.Eventually you will arrive at the best setting for your build, and style of riding.There is not much you can do to improve the front forks.You could try to drain the fork oil and replace with a higher viscosity fork oil.This would lessen the amount of dive when the front brake is applied.Apart from that you would need to see a suspension specialist and change the fork springs, or search for compatible forks off a different brand of bike - but both these options could prove time-consuming and costly.
Regarding poor handling and 'squirmy' back tyre, have you checked the tyre pressures regularly? I weigh in at 65kg and run 29psi in the front tyre, 33psi in the back tyre.These pressures need to be checked at least every 2 weeks, as a drop in pressure in the rear tyre of just 5 or 6psi, will cause similar handling characteristics to those you've described.("squirming").
What is the wheel alignment like? If nuts and bolts were loose after 100klms, the alignment may have been askew as well.Apart from using a stringline, you could take measurements on either side of the adjusters, and ensure the back wheel is tracking straight and the chain is not too tight.Also check spoke tension, as loose spokes will also cause the back end of the bike to move around, and feel very insecure.
Re the 35T rear sprocket, the dealer's email is: brianc@sydneycitymotorcycles.com.au I spoke to him today, and he should be able to supply the sprocket for you.Hope you're able to get everything sorted, as these really are a smooth running and enjoyable bike once they are set up properly.