Square One Dept. A trademark registration for a name or text is usually not limited to a specific font; if that were the case, Nike, Gucci and Coca-Cola would have problems stopping ripoffs. Even if someone registers the word-mark in connection with a design, courts won't limit protection to the design. They will apply common sense to determine whether someone is trading off the mark unfairly and consumers are likely to be confused. So changing colors and fonts doesn't get you off the hook for infringement.
As for your questions ... Assuming someone registered FIRST KISS for t-shirts and cups, they would have priority over subsequent users on similar merchandise and could stop them regardless of the font. You claim that customers "would never be confused." If you can prove that in court, you might be able to get off the hook for infringement, but the The Dear Rich Staff believes that the chances of proving an identical word mark on identical goods does not infringe is little bit like Dr. Richard Kimble finding the one-armed killer.
Trademark fair use. Your second question is a little more complex and relies on interpreting the rules for trademark fair use which we discussed in a previous blog entry. As a general rule, descriptive use of terms is permissible. Again, common sense prevails here since a competitor's repetitive use of a descriptive term may be an illegal attempt to siphon customers.