What is the limit on wording?
The only real limit is sensibility. We don't have a word limit or character limit. However, you'll obviously have more room for text on a 4x6 card than a wallet card. (Generally if we can fit it on a 4x6, we can fit it on a 3.5x5)
As far as the size of the text, the smallest size we normally will use is an 8 pt san serif font such as Arial Narrow or Abadi. This is normally what we would use for addresses and other contact information.