I'm new to this stack , so need some advice, please.
I'm very familiar & comfortable with general Android & embedded SBC flashing & hackery, but ATV's seem a bit of a wild domain.
Which series of ROM are solid (similar to Lineage) and which (affordable) boards/boxes are well-supported? (wiki's not working for me atm)
The Android TV operating system comes readily available in two devices: the powerful NVIDIA Shield TV and the affordable Xiaomi Mi Box. Pick the one that fits your budget and keep it stock. A vast majority of people don't even root their Android TV device because we use it to stream Netflix, Hulu, YouTube, etc. and streaming video works right out of the box with no need to hack it. Even if you wanted to block ads, it's better to do that at the router instead.
If you want suggestions for boxes that run touchscreen Android, then you need to go to an Android box subreddit. We don't recommend those devices here because they were not designed for a living room TV like the Android TV OS was created for.