Long line fishing is a great way to catch crappie. I have done it for years now.
I would suggest at least 10' poles for the guy in the front of the boat and shorter poles for the guy in the back.
You need to find out what works best everytime out when your trying to figure out how far out you need to be.
Also boat speed is very very important. Sometimes 1.2 mph works and other times it's .5 mph so that to is a day to day and sometimes hour to hour thing.
I like to run 1/16 ounce road runners with a southern pro twister and once again color is something that changes all the time. Tip it with a minnow, bee moth or crappie nibbles and your good to go. Also you can run two jigs at a time on one line.
Most important thing is don't stop the trolling motor everytime you hook a fish. This will cause the jigs to fall and probably snag. Also when your going thru the school you want to maintain the same speed so your other pole or partner can catch a fish.
Hope this helps and good luck out there..