dns management. how to predict required # of queries per month?

How cam I predict required # of queries per month?

One of these services says 5 million request per month, how many times would a site visitor request? there are local caches so not sure how to get a rough idea?

Also, these services that are 20-30/year like easydns etc., how many domains do these packages let you manage?

It's tricky... if you want to make sure you don't exceed your limits, one request per page-view should be a good metric. However, the more you know about your visitor patterns and the length of their stays, combined with your TTL preferences, the better you can refine that figure.