Ok wait wait! Are you building this costume from scratch?
Everytime I build a costume I start a huge paper list. I go through each and every part of the character and then I post it. There will inevitably be many more pieces youll need.
Also there are so many ways to build things. I myself am a resin caster so I would build the helmet and cast it. You have a great idea with the Pep files. But i warn you. You need to go the extra mile with Pep and make sure it looks quality. Like many of Galens costumes this requires knowledge of both hard and soft parts.
So get a full turn around 1st and take a heck of a look at him.
I myself don't know what tools you are starting with (do you have sand paper? glues? dremmel? all of these are very helpful!)
What I also recommend is to check out others threads on this build. Ive seen a few other folks making this costume (even recently) so taking a look there will really help.
I feel like i am of little help here, there is just so much going on with this costume.
But i say start a Work in Progress on him now! =D
This costume requires the following practices.
Leatherworking
Seamstressing and tailoring
resin work or plastics
Itll be fun! but all three of those require a different tool and skill set.
Nothing you cant learn! i myself do all 3