That’s correct – for Plex to work, you need one “Server” (could be your PC) that runs the Plex app. This app is the part organizing your media.
This “server” can distribute your content via your network to multiple “client” devices (could be your TV, could be a set-top-box, could be your phone or tablet).
(1a) You can do this using WiFi… if you want to stream higher quality media, it’s recommended to have a wired connection (e.g. from the server to the router and from the router to the client device).
You will be able to start things over WiFi and upgrade it there’s any bottlenecks.
(1b) There’s some TV sets which have the capability to install a Plex client (e.g. some Sony Android TVs but also various LG WebOS / Smart TVs or Samsung Smart TVs) – however not all their models have the capabilities built-in. Generally you might have a better experience with a set-top-box or TV stick (e.g. Apple TV 4 or 4K, Android Fire TV, some Android TV boxes, Roku, Nvidea Shield). If you already got one of those, you can also re-use it for your Plex setup.
Here’s a list of the official Plex client apps.
(1c) see 1b
(2) of sorts. In the first place, Plex is a platform to stream your own content. If you buy a Plex Pass membership, you’ll be able to expand its core functionality in combination with a compatible TV Tuner. This will allow you to watch and record OTA tv from your region.
(3) Plex for its basic functions is free. You can download it and test it out (except for the features you need to pay for). There’s different models to expand the functionality:
- One-time activations for Plex clients on your mobile phone / tablet – those are otherwise restricted
- Subscriptions for 1 month, 1 year or a lifetime pass.
If you want to test it, I recommend starting with a free setup.
If you like what you see, you can test a Plex Pass with a 1 month subscription.
There’s a set of nice support articles and step-by-step guides walking you through the installation and preparation of your media for Plex to recognize it and get you all the additional information like posters, descriptions, cast or online extras (in combination with a Plex Pass).