First I would avoid SMART TV's. as you said you do not need and the idea of someone being able to hack in and watch me wander around in my underwear Well not appealing
Now: All this new stuff.. DON't WORRY ABOUT IT.
How I replaced my MAIN TV (the 2nd one I did not do as neat a job)
I'm in a class A with overhead TV in front.. I removed the "Trim" and measured the WIDTH of the set.. Found a new "Wide screen" of the exact same width, Shorter in height but exact same width.
I then knocked the bottom out of the compartment and raised the "Floor" of the compartment to level Added some masking and it looks factory. Same mounting brackets.. Just a bit of woodwork.
Modern v/s Old technology.
IF watching park cable: Same as it always was. On TV go to MENU and Scan
If watching over the air.. You no longer need a converter.. On TV go to menu and scan.
And that,, is about all there is to it.
NOTE: I did "upgrade" my Winegard Batwing (Sensar III) a bit, Added Wingman and replaced the wall plate with a SENSAR PRO (Way better reception)
Also my system is a bit more complex.. but .. Well. I left those parts out since they are after-market addons (two DVR's and a router that let's 'em chat with each other).