I'd do 125 miles/200kl Loctite the whole bike down plus do a quick oil and filter change - at 500 klm/300 miles same again at 600 mile again. if possible do it yourself. what's it cost you just a few $$$$ and best of all - you know its done. after that its a 1500miles oil/filter job.
these filters you can bulk buy from our host.
I have a 19t on stand by but I am not fitting it to my near new motor till its done a very good run or say 2000 miles. after that I think if you doing a lot of flat running country like I do with very few hills - it sounds good.
so in your case I'd forget the sprocket idea and buy a mottorbat gel battery which will give your plenty of cranking power on tap for those cold morning via the electric start or any other first start of the day and will help look after the dreaded sprag.
apart from an easy run in period following arizoni's guidelines within the forum your on the way to a fun filled adventure plus the start of several posts