One of the great things about Channels is that you can mix and match your sources from time to time, and you keep your library with you. I'm also a Tivo convert from years ago and I find Channels to be the best option. We have been all over the place from Spectrum, Uverse, YTTV, Hulu Live, antenna, etc. Our first foray into live streaming was YTTV and agree with you that its DVR stinks in many ways, but it did introduce us to "record everything you might watch" so you never have to watch commercials. We use Channels that way so have a large library.
There are many things you can use for sources, but you definitely do not have to use cable. HD Homerun with antenna is one option that is essentially free TV once you set it up, but where we moved a year ago we have limited over the air signals. You need to realize that if you use something like YTTV, you will not get a 1 for 1 for all the channels you subscribe to. Channels is able to provide you the TVE (TV Everywhere) channels from your provider. Every provider "pays" for a different selection of TVE channels. TVE is what allows you to run the apps and get live TV, like A&E, USA, etc. If you can add one of those apps to your streaming box and use your YTTV credentials to log in, and you can get live channels via the app, then you will get the channel in Channels. This website has a list of which providers support which TVE channels but I've found its usually not completely accurate and they often provide more - https://thestreamable.com/tv-everywhere-apps . Also, most of them now provide some form of the local channels via TVE. But its sometimes weird like Fox for me only is available at certain times of day.
Remember you can mix many sources. Pluto TV is a great addition is its tons of free TV that normally you have no DVR, but with Channels you now have it all via DVR. Its just not anything that is current.
As for where to run it, as others have said, what NAS do you have as most will run it OK, but some may not. For example the Synology J models are really slow. Personally, I run channels on a 10 year old Mac Mini and don't put it on my Synology. I use the Synology only for storage for Channels. But it will run on nearly anything.
My family has enjoyed that with Channels we can switch providers from time to time and the user interface remains the same and our library stays with us. We have a great collection of movies that have been accumulated from many sources. We do still use the source as well because if its something on a channel that there is no TVE for, then we can't see it on Channels. Like for some reason the Superbowl didn't work on Channels for some reason so we had to watch it on Hulu Live.