Congrats on your new tv! It will definitely be better than your previous E series Vizio. I have the KS series though, but at least you can get some form of HDR.
I would first recommend getting acquainted with HDR:
1 - easiest way to do so is from built in YouTube app. Do a search for "chess HDR demo LG". Play the first video that comes up with most views, then the subsequent "suggested videos"
2 - if you subscribe to Amazon Prime, on Built in app, there a separate category named "4K". Plenty of HDR shows in there from Amazon Originals such as Man in the High Castle, Grand Touring, Mozart in the Jungle
With regards to Roamio, it should work out of the box. I have the Bolt+ and Roamio OTA in the same room with my Samsung KS8500 connected to a non-4K receiver (with a bunch of other devices) then HDMI out from receiver to HDMI 4 0n Samsung (ARC). Then the Samsung k8500 4K UHD player and Xbox One S connected directly to tv (HDMI ports 3 and 2). UHD Color turned on only for 2 and 3, and off for 4.
Roamio OTA I have checked only 1080i and 720p, thus letting the tv doing the upscaling. I do use HDR+ on tv for broadcasts but this is a personal preference. You will be fine with Standard.
One thing to notice is that for some reason TiVo is not recognized from Samsung Smart remote (or whatever they call it). So you will have to manually pick whatever HDMI port you are hooking up the Roamio by going to sources. My suggestion is to keep both tv in the same room for testing. Once Roamio is up and running on old tv, swap the HDMI cable to the new tv , select the relevant HDMI input under Sources on tv, and it should work.
If not, post here and maybe somebody else may come up with a solution, as I would have ran out of one. Sometimes, it can be a very simple thing not done right, and the challenge is figuring it out. Good luck!