I have found this Knowledge Base article to be helpful in setting up firewall whitelists for the default mapping servers. It works well for the default maps. If you end up using a custom map server (such as Google Maps), you'll need to get those addresses added too.
We set it up years ago and seems to have no problems I'm aware of since then. Document what you do. When we brought up a new server, we had to figure it out again. We wasted a bunch of time because we had forgotten about the need for firewall exceptions. Document it well the first time and you'll save yourself time down the road.
Best of luck!