If you got a starter only starter, 6 weeks is a good time. However, most feeds are a start/grow forumulation, here at least, so feed that from day one till 16 weeks old or so.
I do not use vits and electrolites. I only recomend those for the first day after chicks are shipped or if the birds are sick.
Chicks do not have to be vaccinated and if they are from hatcheries, you have to request vaccination. However, they do not reccomend vaccinations for small flock owners.
If you do get a vaccine, it is more stress on the birds, and your future birds should be vaccinated. Why, I am not too fluenty with the mericks vaccine so can't comment much other than you are supposted to make sure all birds in the future are vaccinated. They are carriers for life and the vaccine is a live vaccine. If you get the cocci vaccine, you must not use medicated feed as it will nullify the vaccine.
Good luck!