Sounds like your'e on the right track with the training.
I'd take a serious look at your pack weight of "40-50" pounds. I'm hoping that a lot of that weight is water and not gear.
Spend a lot of time reading through the gear lists on the left hand side of this website and scrutinizing every single piece of your gear. Since there will be three of you going, you can share a lot of the gear (e.g. cooking gear, stove, etc.). You might be able to get by with a large tarp for the three of you.
I've never done the GC, but it is on my bucket list. Use the search feature on forum at the top of this page and set the time frame to 1 year. You should get lots of hits.

Enjoy and be sure and come back with pic's and give us a good trip report. Reports from newbies are always welcome. That's how we all learn(ed).