Forgot to post this..
I have a couple of golden rules for database projects:
1) Never require the code to adjust the structure of the database - columns, types etc
2) Never duplicate data - if it needs duplicating it needs moving out into another table with a foreign key
3) Never store data in a format that can't be sorted by mysql. You may not be planning on it now but at some point you'll want to be able to sort through it as the tables rows grow.
Hope that helps