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.

Miner2049er.