I want a RPi for streaming of TV channels.
Is a RPi good enough? Will it be sluggish going from menu to menu? Can the stream be played fine at 720p or 1080p?
First..."a" RPi is not very specific. Your thread title asks about RPi Zero W which might not be powerfull enough. A RPi2/3 might be better in all regards.
1080p shouldn' be a problem for the RPi 0w, but I'm not sure if it comes to live-tv streaming. And not sure how good the wifi module really is
Is it expected that the current status can continue for future versions of the software?
What? Do you mean if it works now, will it work for a later LibreELEC version? Are you really asking us if your RPi will still be supported in, say, 10 years?
Can I command the OpenELEC Kodi with a cheap universal remote control? Are there a recommended setup guide for this?
sure....it might depend on what kind of hardware you are running OpenELEC. But...this isn't an OpenELEC forum. If you have question related to OpenELEC, please visit: OpenELEC Mediacenter - Home
Look for a Mini wifi keyboard such as one from Rii.
I have used them for several years, and have supplied close to 50 of them to friends, they work without problem on pi3 and LE.
Depending on which system you are, you are also able to use some remote app from your smartphone. There is "Yatse" and/or "Kore" for Android devices and a bunch for iOS devices as well.
There is also the Flirc dongle (which is a thing I use myself). With that you are able to use ANY IR remote you own. There are many how-to videos for the Flirc dongle on Youtube.
If the remote you already ordered doesn't fit your needs, then I would take a look at Flirc 
Depending on which system you are, you are also able to use some remote app from your smartphone. There is "Yatse" and/or "Kore" for Android devices and a bunch for iOS devices as well.
There is also the Flirc dongle (which is a thing I use myself). With that you are able to use ANY IR remote you own. There are many how-to videos for the Flirc dongle on Youtube.
If the remote you already ordered doesn't fit your needs, then I would take a look at Flirc
If you are OK at soldering - then you can add a ~$1 TSOP to the GPIO pins of a Raspberry Pi and that will get you support for lots of IR remotes too.
I added one to a Pi Zero W for a minimalist LibreElec build (the official Pi Case for the Zero W has a camera lid with a hole perfect for a TSOP to be glued in to! Made a very neat little box for use with a cheap IR remote. (I used one that came with a USB TV Tuner a while back)
I've got a first gen Flirc, and it's very nice, but it costs more than twice the price of a Pi Zero W - so for a low cost build, a GPIO IR receiver can be a good fit.
So, to be more precise, about the remote control. For a Panasonic TV, although it has VIERA, I searched for CEC and didn't find the option to enable it
I have a couple of older Viera's - 'Viera link' is what they call their cec implementation.
