Should I store my intellectual property / code online?

You're not being paranoid at all. First and foremost you must consider requiring a VPN (and maybe 2 factor authentication) to access your company data/intranet. Passwords should be stored in absolutely nothing less than an application like KeePass or LastPass.

I am a huge fan of a Wiki. But you need to draw a line between what is "the internet" and what is "our private network" - Anything you put on "the internet" should not be intellectual property. The internet is a public place no matter how you look at it.

Secure your network and your websites and data behind it will be secured also.

VPN + Wiki on Apache/IIS with proper IP restrictions + KeePass and you're good to go

What I typically see for high value intellectual property that needs to be accessible to a global team is:

• A dedicated server (to reduce the risk of attack from other services or applications on - that server)
• Its own DMZ (again, to segregate it from other servers)
• A VPN with strong authentication controlling access to that DMZ

Then whether you decide to use a wiki or other form of information sharing is up to you.