Will adding Roku to my LG result in any loss of picture quality?
No, so long as the Roku supports same or higher resolution as the TV. For instance, if it's a 4K TV, you'll want to get a 4K Roku.
Will my Roku account enable me to sync settings, lists, favorites, etc. between the two televisions?
What do you mean? Settings are per device. As for lists, favorites, I don't understand the question. Roku doesn't have that. Apps within Roku do, and you should be experiencing that within any app that supports it.
What Roku product should I be considering for the LG?
Any of the current models should be fine. If it's a 4K TV, you might want to get a 4K Roku device, which relates to question 1.
What other considerations are there that I don't even know to ask about??
You already have a Roku, and know pretty much how it will work. The difference between Roku TV and standard Roku devices are that the Roku interface includes TV inputs on the Roku TV. With a standard device, the Roku is plugged into one of the inputs, and it doesn't interact with the other inputs.
Roku Community Streaming Expert
Note: I am not a Roku employee.
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