Hi there, welcome to the community.
Can you please update your profile on here if you haven't already, to contain your landline number and such to allow TalkTalk staff to identify you and access your account.
Next, I need you to go into your YouView settings, and post the last 4 digits of your device identifier code, so that this box can be set as primary. You can find this code by doing the following: Y Button> Settings > System Information > Device Information
It will take a couple of days for someone to get to your post but they will make the relewant account changes for you and set it to the primary box.
I have the TalkTalk TV Service operating from my Humax YouView box. It works absolutely fine. The TV Light doesn't come on because normally the router and YouView box are both made by Huawei and are specially made to work together, prioritisng TV data traffic to make sure there is never any break up when watching boost channels and such. If you have a fibre connection (which I assume you do, having a HG635) then that isn't really too much of a problem that the light won't come on, and rest assured that it will still work absolutely fine.
Do bear in mind however, that if you have any problems with your TV service, you will not be able to get the full level of support from customer services, as they only officially support the Huawei DN360T, DN370T and DN372T set top boxes.