As Barb135 stated this is not something to be overly concerned about, but it's best not to make a habit of missing medications. Begin taking the medication at the prescribed dose and don't add "extra" to make up for the missed doses.
Not a whole lot. Levo has a long 1/2 life, so it stays in your system for quite a while; missing a couple of days isn't going to hurt much, so long as you get back on them right away.
It's important to take your medication every day, as close to the same time, as possible.