The status Network: Firewalled means that your I2P client is unable to listen for inbound connections, which may affect your performance negatively a little, but it won't prevent I2P from working in any way. Normally you have to set up port-forwarding on your router to solve this, but Tails' firewall would prevent that any way. It's not important.

Note that it takes some time for the "I2P HTTP Proxy" (which is used when accessing .i2p sites in Tails) to get ready even after bootstrapping is finished. I'd say it definitely should work after 15 minutes, otherwise you have encountered some kind of bug. You can check it's status (which should be "Running" when it's working) in the I2P Tunnel Manager from I2P's router console.