Thanks for sharing your experience! I would love to learn more about how you've chosen to approach your need. Are you populating a participants list and then doing your counting and filtering in your forms? This would be similar to what I described in this post.
Do you have multiple data collectors in your case? If so, how are you managing the possibility of some of them going offline? Do you ask them to make sure they refresh right before each new form filling session? Are your quotas strict or is it not a big deal if you go over by a couple of participants because a data collector didn't get the latest entity list version?