Welcome to the forum
Regarding your questions: - yes it looks like a good deal. If it's in good shape and well maintained.
New cost is about $3200 as far as I know. Plus whatever the dealer charges for delivery etc.
The sprocket: it does take away some of the top speed. Based on that I never did it.
Life (mileage) expectancy: once i heard a rule of thumb, multiply a bike cc's by 100. That will give you 24,900 miles.
There is a thread somewhere here where people posted their mileage.
How to make it last: download the maintenance manual from this site, and follow the instructions.
Keep the shiny side up ! :rawk: