Host based content blockers have no future. Ad companies have been moving to first-party ad delivery in the past few years, and YouTube serves ads and videos from the same host.

Edit: nevermind, I've completely misread your comment to be about Pi-hole :)

I think OP says connect Pi via HDMI and don't use TV at all (other than switching to HDMI), he does not mean use Pi as an adblocker at dns level

Correct.

Are there remotes for Pi? How do you control it? What tv like OS do you use?

Can it also turn on/off tv? I think HDMI allows that but not sure if Pi can do that

There are lots of USB-IR remote receivers. The nicest, in my opinion, is the Flirc (flirc.tv) which has all the smarts in the USB dongle to convert IR remote signals into a simulated keyboard. It's reasonably cheap, too. I like using a TiVO remote, because their ergonomics are almost perfect.

To turn on and off a TV you need an HDMI port that supports CEC. The Pi does, so you just need to install cec-client.

As for OS, you should use the general purpose Linux distro that you are most familiar with. If in doubt, use Gunnar Wolf's Debian for Pi, which is as close as you can get to 100% Debian on a Pi.