I am very excited to start my first post to establish my WIP on The Dented Helmet for Zam Wessell. I have been researching many things. Printed off over 100 reference pictures from many of the Zams before me. I have received good input from the Texas Panhandle Star Wars Costuming & Props group of 501st and Rebel Legion members. Just ordered the Greebles from Pink Wessell - my Christmas present to me! Hope to post lots of progress soon.
Good luck! It's time intensive. Cost too. But a really neat costume when you got it finished. I've been on it nearly a year, and all I need are some changes and gauntlets. To be fair, I'd be done if I hadn't spent time on two Star Wars children's costumes and their Jedi robes. I doubt it will take you as long.
Not sure if this bit of advice will help you, but take full advantage of spring and summer weather if you plan to airbrush your leather or use anything with strong fumes. Some of this can be pretty messy and I found it best to be outside.