The Call for Votes should include clear instructions on how to cast a vote. If it's easier for you or your administrator, two separate addresses can be used to mail yes and no votes to, providing that they're on the same machine. The voting period can last between 21 and 31 days, no matter what the preliminary results of the vote are. The charter can't change in mid-vote. One way to avoid this is to create one large list of everyone who's voted, and sort it in alphabetical order.
Every vote is autonomous.
The votes for or against one group can't be transferred to another, similar proposal. A vote can only count for the exact proposal that it was a response to. The wording doesn't have to be exact, your intention just has to be clear.