Not sure how to find the Time Capsule model. It should be the last major update, I think (it's the tower shape) and it has wifi a/c which I believe is the fastest option they ever offered).
Haven't looked at Airport Setup - after getting overloaded earlier today, I just stopped trying to figure things out for the rest of the day. I probably don't understand much about Airport setup either. Somehow I got it working years ago on another Time Capsule and when I got the new one, I think it asked if I wanted to use my prior settings. So I didn't understand what I was doing originally and what little I may have picked up, I've certainly forgotten.
My external drives at that MacOS journalled (or something like that). But I was doing my later efforts by using a thumb drive plugged into the cable provider's router. Not sure what that has. I'll have to check that out Sunday.
In all my looking, at the TCP/IP when I select the cable company router it has two main sections. For "Configure IPv4" and "using DHCP, it has:
The second section says "Configure IPv6" which says "automatically". The Router, IPv6 Address, and Prefix Length are all empty.
I have not found any way to get two different sets of numbers (one for each router) so maybe because of bridge mode?
The things I've seen refer to the router number, I think, not the IP number.
All Greek to me. I just never got into all this stuff. I could do a lot of stuff on computers in earlier days when it was often hard to find software to do what I wanted. But by the time all this other stuff became common, I just didn't need to figure things out much for myself and certainly not enough to remember later!