If you're itching to play and fiddle about with your brand spankin' new machine, then I'd say wait to calibrate the battery as to do so properly would require some no-play time (IIRC).
As for re-installing the OS, is there a particular reason why you'd care to do so? I know that I wanted to for my MB because there are apps and assorted items that I knew I wouldn't need or want (printer drivers, extra languages, etc.) and so doing an "Erase & Install" made sense to me.