Hi Damian,
How many different products/8-digit numbers do you have? Are they standard/static (i.e. don't change), or are they generated as a unique item number for each registrant?
You can set up the textfield to be integers only. To do so, check 'Validation Required'at the bottom of the textfield element's screen, click on 'Library' and then select "ff_integer" to restrict it to numbers only if that's how they're set up.
Within the textfield, you could also limit the number of characters to 8, but that might not be the best way to do it if you have a limited set of product numbers. (In that case, I'd probably go with a select-list for them to choose from.)
And finally, yes, you can set up the form to send a copy to the registrant. Go to Form Properties -> Advanced tab, and check Mailback or Mailback as sender. (Mailback as sender will show the registrant's email address as the 'From' field. Mailback will send them a copy.)
Hope this helps...
Terry
BreezingForms Customer Care