I've got a bunch of questions and thoughts regarding promotion of my website using flyers, but I will start off with a couple of related questions.

I plan to print on each flyer a unique number - which can be entered at my website, and serve many useful purposes - such as tracking responses, and also as an entry into a sweepstakes.

(Q1) PRINTING COMPANIES. I've started to send out enquiry emails to printers, but has anyone had experience of doing the same or a similar thing with flyers and if so, how did you do it? One local printer I phoned recently said they could accept an Excel file of all my numbers (thousands of them), and print each one to a different flyer.

(Q2) NUMBERING SYSTEM. Although internal to my DB, numbering will be sequential, I DON'T plan on the printed numbers being sequential 0001, 0002 ... 5000 etc. The number that GETS PRINTED on a flyer will be a sequential number encoded using some algorithm plus a checksum digit (like credit cards.) This is so that if a visitor enters it incorrectly they get informed of a bad digit somewhere. My question is - how do I decide on an appropriate numbering system? I don't want too few digits, or too many. For example, UPC codes are usually 12 digits, US phone numbers and eBay item codes are 10 digits, and a number of credit cards are 16 digits. And I may also want the numbering system to be expandable in the future - say I choose 8 digits now, but go to 12 digits in the future, but still want the new system to be backwards compatible with the previous system.

Any advice and/or pointers would be appreciated regarding these two questions. Thanks in advance for any replies.