So...do we create our own characters for that one week? Or a character for every week?
Either option is fine. What people have been doing is making one character and playing it through or asking Sam, who DMs the game, if they can switch characters between chapters. Remember though, the characters must be made using the new D&D Essentials rules, not the normal 4e rules.
Or are there pre-made characters?
There are six different level 1 premade characters to choose from if you do not want to make a character of your own. All of them are decent. Wizards of the Coast may have updated them to level 2 but I am not sure.
And Do you think there will be people there who might want to start a group?
It is certainly possible. We have seen MANY different / new players come through and play in a session of D&D Encounters. Some of them play every week. They may be interested in starting a group of their own or even branch off and run D&D Encounters on their own. The limiting factor seems to be a lack of interested DMs.
I highly recommend coming down to Plainville to check it out. The people that play are all super nice and great to be around. Sam, one of the employees there and the guy who runs the game, is a rock star when it comes to helping new players, DMing the game, and making it fun for everyone.
If you're looking to meet new players and get yourself into a group this is something you should strongly consider.