Helix internet with modem other than Helix Gateway?

I just installed Helix router this weekend, I also notice like you extra ssid, I did not go for the bridge mode to start with, and see if by using port forwarding I can still access my own vpn server which I can.

I saw in fact 4 ssid in 2.4ghz (3 hiddens and 1 with ssid I configured) and 3 ssid in 5Ghz (2 hiddens 1 I configured), I believe the hidden ssid like you said are used for the helix tv, they probably have a well-known ssid but hidden for the helixtv to connect to as I did not configure the helixtv box and magically it connected to the helix router. 

One thing I notice was there are ssid with 802.1x authentication, one on each band. 

By the way, 4 ssid are not that bad in term of congestion/interference, trust me I worked 10+ years in wifi for HP and Aruba working at firmware level.

The Helix wifi router is not that bad, although one notch below Bell as Bell router has 3 radios, 1 2.4 and 2 5G, both use Quantenna chipset, it is not the best but for consumer it is ok.

The configuration you can make to wifi is almost none, beside channel selection and ssid name, probably to avoid user to mess with config.

So far so good for me the new Helix router, Videotron did not do a big investigation, they just pick the one Comcast use.

My only rant is even thought the new Helix router has phone port, it does not work "yet", I call support and they said I have to keep using the old Harris cable modem for the house phone, go figure!  Again one more point for Bell, one big monster router with everything (phone,tv,internet), so now we have 2 cable modems.

I wonder why you not want to use the Helix router beside MOCA does not work and multiple ssid thing?

If you are like me, I have a very huge home network (43+ devices) that support all the wifi switch/plug/sensor/camera I keep on my old wifi router ASUS AC68P that is connected to eth1 of Helix, it is a double nat but as I said, I am able to port forward 1194 to my old router for vpn server and it is working.

I cross my finger because of covid we all work from home and the last thing I want to do is troubleshoot the Helix router.

Not really answering your question with my long reply 8-)