Hello! (: Here's my 2 cents. (:
Shirt: Yes altering a pattern would work. Also what would work is making the shirt out of the white fabric then appliqueing/top stitching on the reds. I would use a cotton for this.
The skirt is pretty simple as you said, be sure to put the bias on first! It would be hard otherwise.
For most sailor fuku with sleeves/shoulders like that I would use organza, but those look like craft foam might work best. I would attach them with velcro. (:
For the collar and the bow I would say use a cotton. Again for most fuku I would use a satin, but I think that would look a little funny with the rest of the outfit being matte/cotton.
I have no clue for the glasses though. ^^
Good luck! (: Hope this helped!