So I have gone ahead, purchased and setup a GW1003. For those who are interested I have a few observations.
- The product seems well built and is fairly trivial to assemble. The manual is okay.
- There are multiple IOS apps to choose from for setup of the gateway itself. I initially chose Ecowitt, which at at least on an iPad (IOS 15) was not able to register with Ecowitt. I registered on the website and used the app on an iPhone (IOS 12) to setup the GW1003.
After adding a rule in my firewall to block external access by the GW1003, the Ecowitt app changed to Offline. This app requires access to the ecowitt servers.
I installed one of the two other IOS apps, WS View Plus. This actually seems to be better for device setup, although the current weather page is basic, esp compared to the Ecowitt app.
Once I had disabled ecowitt.net as a weather service the GW1003 was connecting to NTP servers, which I had allowed, but nothing else.
So in answer to my original question, access to the internet is required for the GW1003 for time updating, and for firmware updates, which the app is nagging me about.. Also according to this forum post, https://www.ecowitt.com/shop/forum/forumDetails/189, the gateway will reconnect wifi. I do not think this is happening in my case.
I will see how the sensors go for reliability with all of them working out of the box.
Next step is to set up a custom weather server!
Jon