Everyone has different opinions on line length. There are numerous calculators that are supposed to give you what you need. That being said, I'd recommend (and I'm not the only one) to use 10' minimum lines starting out.
For the shank length, it depends on your collar thickness. I use 2" wood (1 1/2" thick) and have three inch shanks. They are just long enough to work and not extend too far into the keezer.
Make Beer, Not War.