I would get her to the February show and get at least one or two kitten shows in before she is 8 months and goes to the alter class.
The cages that are provided by the club will have the size on the flyer. Usually I just use a few matching towels and some clips to put them up (3 for the sides, one on the top, one on the bottom).
Have you been practicing show handling at home? Stretching her out, letting her stand on 2 back feet on the table, getting her to sit facing away from you and holding her head for examining profile, etc.? Be sure to also get her to play with hand toys (feathers, sparkly things, etc.).