I'd just let em go. Don't transplant yet, and let all the bines grow so they can get a lot of leaves to help the roots get established. They probably won't grow a ton higher this year, but I would find a spot with more vertical room. My second year Centennial, that I started in pots just like you, made it to the top of my 16' trellis by the beginning of June. As far as twine, I just use heavy jute twine. It's cheap and holds up for a season. I just string new twine for the following year.
Screw it, Lets brew it
Primary 1- BM's Cream of three crops.
Primary 2- Paleface Scalper
Primary 3- Monks Reward (Kreuzberg)
Kegged - Honey Badger, Heady topper clone 1, Indian Paleface Scalper
Bottled- Skeptical Dog winter Lager, Hell's Belgian, Old Dutch Hiefer Hefe,Aphlewein, Chocolate Thunder porter, Jacked up lantern