I think by default all you need is to set the host to "localhost" and the port to "8888". If that doesn't work, check the Tools > Options > Connections tab within Fiddler for the port number.

We haven't heard any other complaints, so it leads me to think it's either your end (proxy?) or npm's end (blocking). We have no idea what their blocking mechanism could look like. For all we know, they could be doing agent-string filtering, and blocking requests from ProGet software, but not your web browser or npm client. Best bet is to run ProGet through a proxy (like fiddler or wireshark), by going to Admin > Proxy. Then you can see exact traffic.

The homepage will attempt to connect to inedo.com to download latest news, and it will also connect to the database to provide a summary of feeds (dashboard). However, if either of those operations times out, then you should get a prompt error. Maybe, for some reason, the request isn't even being routed to ProGet. You can connect ProGet to a proxy like Fiddler (Admin > Proxy), and then attach to SQL Server to see if anything is timing out..