You would be forwarding ingress traffic(traffic not originating from your internal network) to 443/80, this doesn’t affect egress requests(requests from users inside your network requesting external sites) so it wouldn’t break your internal DNS resolution of sites. All traffic heading to your router from outside origins would be pushed to your reverse proxy where you can then route however you please to whatever machine/port your apps live on.

Probably an issue on the device, I would try clearing the cache for the application and see if it fixes the issue. Often times weird stuff like this is some web component that cached incorrectly.

The CenturyLink fiber plan is pretty nice, me and my brother in law are on it and it runs as advertised and I’ve had maybe 2 outages in the 3 years I’ve had it, unlike my previous provider where it would be like 1 per quarter