why not use other pre-gens besides those in the comics? the book and box-set supplement has a number of other pre-gens to select from. you could easily create a few additional pre-gens with about thirty minutes of work for each during a week.
When I've taught the game, I've followed a similar pattern of offering pre-gen characters to the players then teaching them to make a character later on. Most of the time I do it after the first winter session. That gives the group a chance to see how the mice grow and change over time, so they make a character with some ideas of growth in mind.
Running a group of six will necessarily provide them some added strength in helping dice and borrowed gear. It will reduce the pace of characters making growth.
In fact, I would recommend that you offer for most of the team to play Guardmouse ranked characters--only allow one to play a Patrol Leader or Patrol Guard as leader. I wouldn't consider letting someone play Celanawe; I'm not likely to let someone play Saxon, Kenzie, Sadie, or Leiam. I would create other pre-gens that can make a unique story with unique personalities.
Also, when making pre-gens, I do fill in the parents, artisan, mentor, friend and enemy as well as cloak color. I leave the BIG and Gear up to the player. I make sure to have 1-3 sentences to describe what I imainged when building the pre-gen. For most that has helped the player form a sense of who the mouse is and helped them settle into the group.
-- The Guard Prevail --