To answer your questions in order:
Question 1: Generally, people will start with a smaller starter when they have only a very small amount of yeast to build from. If you are working with 50 to 100 billion cells from a typical pitch of Wyeast or White Labs, you will have enough to go straight to a 2 liter starter.
Question 2: Pitching the full starter volume is a matter of personal preference. Generally, I make my starters well in advance and cold crash them to decant most of the starter beer off the yeast cake. I am also overbuilding my starters to save some of the yeast cells for teh next brew. If you go for a vitality starter, you are making your starter just 12 hours give or take from the time you need to pitch it and then pitching the whole starter wort, beer and yeast into the carboy with the freshly made wort when the starter is at high krausen.