Buy a Raspi 4 or 5 if you can get it. Canakit has slightly overpriced but compreshsive kits. Digikey tends to get raspi 5s faster then other stores if you want the latest and greatest, but it’s a b2b company that is kinda annoying to buy from as a retail customer. A 4gb model is all you need from either gen. Keep to a 32gb or larger sd card.

Install libreelec as the operating system. They have a usb program that will flash a usb drive to do this for you. It will automatically boot into kodi, which in is a linux based media center. You can then point kodi to any file server you have, or plug in a usb drive into the raspi with your movies/shows. Kodi aslo has great addons, so you can add things like youtube/nebula/etc.

For advanced use, setup jellyfin on a home server, then use the jellyfin kodi addon to sync all your media. This is really nice when you have kodi setup on multiple tvs, as it will sync when you pause shows/movies, can auto skip intros, stream live tv and make sure all your systems are up to date about with what media you have available.

For a great universal remote, buy a flirc ir recivever that plugs into usb and a flirc skip remote. Flirc is a great company in this space.