One would need to vote on the "indefinite postponement" motion first. Then, whether or not that motion passes (makes no difference to subsequent main motion), you can go on to the main motion and vote no.
The indef postponement only applies to that current session of course, in any event.
Nope, I've been a "town meeting member" for 41 years (open town meeting) and only missed a handful of nights. We only vote once. "Indefinite Postponement" is used to kill a proposal. Yes, it can be brought up at another town meeting on another date, but it has to go thru the same process all over again and most never even try the 2nd time.