I've connected my Apple AirPort Extreme to it and it works great. No set up required. I'm sure if you connect the ac 1900 router to it and connect the time capsule it should be fine. The modem is ore programmed and its a plug and go. The modem is not so much hardware compliant but more towards Internet provider settings. So when a router is connected to it , it automatically retrieves the provider settings. Hope this helps
Works fine with my Apple Airport Extreme but cannot answer for the other kit. It's fairly simple technology and their support is good so I wouldn't have thought there would be a problem. Have you tried contacting them via their website.
Yes, according to the specs for that router it supports PPPoE wan authentication, this modem will allow you to offset the authentication to your router (which I guess you are trying to do with a UK ISP and DSL. The time capsule will work fine per above comments.