I found that the plastic tubing was longer than I needed for my current project, but just let it "dangle" because I was afraid that I'd short myself for the next project. But it really didn't cause much problem being too long. Well, you can get more plastic tubing for really cheap from Grace, and that way I can have pieces for whatever size project I'm working on.
I have used it for 6 months, and now wonder if the piece of plastic tubing really has to be in one piece. I think it would work just fine to have two pieces butted together along one side.
I also found that I needed different lengths of leader cloths. They included some white cloth that was plenty long. So I used up some ugly cloth that won't be caught sewn into one of my quilts, and made another set of leader cloths for baby size quilts, rather than cut the white leader that was included.
I wish I knew where I could buy additional plastic tubing locally, but haven't really looked yet. Lowes would be my first guess.
So my suggestion would be to not cut the plastic tubing until you are comfortable doing so. But even if you do cut it, having it in one long piece is not a necessity.
P.S. I LOVE my Grace frame - one of the best purchases I've made. Don't know why I struggled with actually getting one for so long. Sara