New (Noob) Member Help Appriciated

Hi guys I've been checking out these forums for a couple of weeks after deciding to make my own Boba Fett costume. Normally I wouldn't make a post but you guys seem like a great community, which I would like to be a part of.
I've been doing a lot of research on how I'm going to accomplish my costume and have a vague idea on how it may be accomplished. I want to make my costume entirely from scratch primarily due to lack of funding. (Money is tight as a student:cry)

Just a few things that I would like advice on:

• So I'm making my helmet out of cardboard following a template. Looking at tutorials, once that is accomplished I need to cover the helmet in filler? Can anyone recommend a decent filler that would be suitable for this?
• On the subject of filler the tutorials I am looking at say,"After every layer sand and re-apply". I'm probably being really stupid as usual but how exactly would sanding it give it a smooth finish? And what would I use to sand it?
• After that's out the way I'm planning on silver spraying the helmet (and armour) to give it a metallic look. What sort of paint would I use to go over the silver to keep it looking metallic? Do I have to use a certain type of paint or will any paint do? (Please correct me if the silver is un-needed!)
• Again with painting, is this: The page you requested cannot be found! the right colour for the helmet and armour? (I'm partially colour blind which doesn't help lol)
• Finally, I was planning on using sintra pvc sheets for the armour. Living in the UK the costs for shipping is extortionate so is there any UK based sites that sell anything similar?

I appreciate any advice that any of you give me in starting this project, bare with me if I have forgot anything.
PS - I have a GCSE in Resistant materials so I have a (very) basic knowledge of how to create the armour.

Thanks all
Sam.