You can apply for a new US passport or passport renewal and a US passport card at the same time. This is a convenient option for frequent travelers to have both a valid passport for air travel and a passport card for travel to these destinations by land or sea.
As for when you should use a Seal... use Master Seals on non-promoted classes at level 10 to upgrade them, and Second Seals on non-promoted classes at 10 to switch them over to another class tree (mostly worthless, though switching characters that have access to Mercenary, such as the Avatar, over to it ASAP is generally a good idea), or to switch a promoted class into another promoted class at level 15.
When you find a master seal, you might want to use it on your level 10 or higher unit. Don't. Every time you level up, you get stat boosts, right? When you use a master seal too early, you miss those stat boosts. For example, say your unit is level 10. If you use a master seal, you get good stat boosts, but you miss level 11-20 stat boosts. So wait for level 20. I know it's hard to wait, but the best always come later. Now, the master seals and second seals are very confusing.