I'd be concerned about trying to send thousands using our mail plugins, and maybe even hundreds, depending on what mail method you use in J!, how fast your server is, how well linked it is to the 'net, etc.
The challenges and issues involved with real "mass mailing" are not trivial, and Fabrik isn't really designed to provide a complete mass mailing solution. We can handle smaller mailings, in the tens or hundreds, but trying to send to thousands of addresses would almost certainly be problematic. We also don't provide any of the "feedback" you get with purpose built mass mailing products, i.e. information on bounced emails, etc.
There are a number of J! extensions which are designed to true mass mailers, and a few "bridges" to third party mailing solutions like MailChimp.
You can certainly try using our email cron (scheduled task) plugin, which provides basic functionality for sending to a table of recipients, using standard placeholders for the "to", "subject" and "message" fields, and should be fairly self explanatory on setting up if you read the tooltips. But because our 'cron' tasks run as part of the standard J! page load processing, trying to mail to "too many" recipients is going to run in to PHP processing time limits.
My advice is that you investigate some other component that specializes in mass mailing, but which can still use configurable tables and table fields for driving the address list.
-- hugh