I'm building a touring bike, and while looking for some new ferrules for the cable outers I hit a few problems.

I really want some silver/chrome coloured ones. I can find some nice metal ones in 5mm, but only plastic in 4mm unless I want to spend (relatively) silly money.

So, my questions:

1. Can I use 5mm metal ferrules on gear cables?
2. If not, where can I get 4mm metal ferrules that aren't crazy expensive?
3. I've heard that plastic ones are actually better anyway (something to do with making a more watertight seal). Is this true?
4. Do I need to crimp metal ferrules?

It's a small part of the bike, but I want to do it right....


Thanks in advance!