You shouldn't cover your pot during the boil-
According to How to Brew by John Palmer-
Once you achieve a boil, only partially cover the pot, if at all. Why? Because in wort there are sulfur compounds that evolve and boil off. If they aren't removed during the boil, the can form dimethyl sulfide which contributes a cooked cabbage or corn-like flavor to the beer. If the cover is left on the pot, or left on such that the condensate from the lid can drip back in, then these flavors will have a much greater chance of showing up in the finished beer.
So, just watch it so it doesn't boil over. After the hot break, there is less chance of boil over.
I've used smack packs and they get pretty swollen up. After the pack swells, I make my starter and then pitch it a couple of days later. So, I would smack the pack about 2-3 days before brewday, and make the starter. If your haven't made a starter, you might have a longer lag time before fermentation takes off. When the wort is cooled (70 degrees or so), go ahead and pitch your yeast.