Is the 5 GB traffic limit per IP or shared across all 5 IPs?

The 5 GB traffic limit is shared across all 5 IPs per user per month. Traffic limit renews with a new billing cycle so you can use free IPs every month.

What happens if you go over the 5 GB traffic limit in a month?

If you exceed the 5 GB limit, your access to the proxies will be stopped until the monthly traffic resets at the beginning of the next billing cycle.