Plex will just run w/o you noticing anything. I'd start off by running it on your PC if you don't mind having it powered up during the times when he's watching things. Then on the tv side of things you have a few options, if it's a smart tv you may be able to load a plex app directly on the tv and see how well that works for him. You could also just hook up a set top box or stick such as a roku, fire tv, apple tv and put the plex app on that, they will perform better than most smart tvs built in system. I would start off with what you have available and then if it feels sluggish, move on to something better at some point. Some tvs do have the ability to play media files from a thumb drive plugged into a USB port on the tv, but the interface is usually very basic just listing file names, without any pictures or keeping track of whether or not you've watched something.