When I did my reach suit it was my first foam build also. I tried to make my thread kind of step by step, so I'd recommend you follow through it.
Sean Anwalt's Mk V build
Turbocharizard has a build thread that is awesome as well, and definitely way more chock full of experience.
TurboCharizard's Halo Reach CQB Build Log
I will say, with great emphasis, you NEED to have SHARP BLADES and a Sharpener. That is imperative. Lol
Published props, evil Ted, and others have great tutorials on YouTube for working with foam. Definitely look them up.
Otherwise, keep us posted with updates! Great group of guys on here always willing to help.