Looks like if 3 people don't like you, there is a potential you're getting kicked, because that's all you need to get a vote going.
That's a little like saying if you're American-born and over 35, there is a potential you're getting elected President. Just because the bare minimum requirements are met for being a candidate doesn't mean you're likely to get the vote.
If a poll opens considering ostracism for a Citizen, there's no reason to expect a majority of the Ecclesia to support kicking that person for the hell of it or out of despotism. Since pretty much anyone can be a Citizen and participate in these votes, it seems to me highly unlikely that anyone would be ostracized without good reason.
If they fail, what stops them from getting another vote going? How often can these votes be created?
These points have not yet been considered, as far as I am aware. I agree that it would be good to limit how soon ostracism can come up again for the same Citizen as this avoids a small contingent from opening repeated votes as a harassment tactic.