You would need the hotspot feature to share the connection with other devices, but that might force you off of unlimited data- I may be incorrect here, but I know on AT&T if you're on unlimited data you don't get tethering/hotspot or FaceTime over 3G/LTE.
The hotspot is $20/month for 2GB. Wait for iOS6 to get the jailbreak, then you can buy TetherMe ($5) to enable the hotspot without paying the rip off price.
I have TetherMe on my jailbroken iPhone4 and I use the hotspot feature all the time; it just shows up as cellular data (as it should!).
Verizon had Apple disable the hotspot feature. They have it set so that it can be enabled once you sign up for the separate hotspot plan (it won't affect your unlimited data plan). Basically, it turns the tethering feature on and then sets a different APN record--that's how Verizon differentiates your iPhone's data from the tethering data/hotspot. Wireless carriers wanted this so they could gouge customers for more money.
I'm waiting for iOS 6 jailbreak to come out before I buy the iPhone 5 (at full price).
You're not going to be able to use the iPhone as a router per se. The hotspot allows 5 devices to connect (someone correct me if I'm wrong). What you could do is use a router which has DDWRT on it, set it to connect to the iPhone's hotspot (whenever it's available), then set your other devices to connect to the router, not the iPhone. This method will allow you to overcome the 5 devices limit.
In actuality, if you do manage to get this working, Verizon will either throttle you once you use a certain amount of data or drop you completely as a customer if you repeatedly use a lot of bandwidth.