I’ve been using something similar for a long time. Currently a 2018 Mac Mini sits under the TV, a 65” Sony Smart one. A surrond sound amp takes an optical digital feed off the back of the TV. The Mac Mini HDMI does video and sound out in the one cable, very handy, the previous one didn’t. A Drobo with 5 x 14tb is a big bucket for all our video assets and other material, hangs off a USB port. All is controled with a Harmony remote, which is great. Remote Buddy on the Mac helps a bit too.
Most of the time I just press a button on the remote, it switches everything on, and Remote Buddy fires up Plex and away we go watching whatever we have stored on the Drobo. Works well! I find Plex great as it curates movies, tv shows, etc; remembering where you are in a particular programme if you switch off before the end of the episode, etc.
Another option is to ‘Watch TV’. Again the Harmony remote is programmed with a different button / command to switch everything on, but finish in the smart tv interface on the tv itself. Here we mostly go to the BBC iPlayer and watch something there, we really never do watch ‘live tv’ as there isn't a ‘pause‘ button! I find it best to think of the Smart Tv as a big iPad rather than a conventional display of a live stream from somewhere.
We do have a Plex player client app on the Sony, so selecting this will access all of our Plex library from the Sony menu.
This doesn’t work all the time, so we tend to use the Plex client directly from the Mac Mini. which is running the Plex server too. This can also be viewed from any Plex client on any device in the house.
I’ve used EyeTV satellite tuner for a long time too. I mostly use it to record TV programmes for later viewing on Plex. It can record 2 satellite streams at once. With streaming and the like this is beommig less and less necessary over time.
I can use the Mac Mini as a ‘huge computer’. I have a BT keyboard and trackpad nearby (joined together, so can be used on your lap) but I tend not to use it much this way. I mainly do Mac Mini housekeeping using the iOS App ‘Screens’ on all of my iPads and iPhones so I can remote control the Mac very easily from anywhere, even away from home.
The Harmony remote is key really. Once setup anyone in the house can get the TV / Mac Mini / Suround Sound / Plex up and running in one keypress. Same with one keypress (the other one!) and start watching BBC iPlayer on the big screen with pause / play on the one remote. All very good for me and the family.
Photos for me is different. I tend to just use Apple’s cloud and share photos in albums, etc if necessary directly to other people to their phones/computers.
Sounds: the same, I‘ll use Airplay to share sound in a few rooms if necessary, parties, etc.
There is a screen mirroring app on the Sony TV so we can ‘cast’ photos to that if we want to view them collectively, they do look good on a big screen 😎. Visitors can easily cast their photos too.
We’ve even cast Zoom meetings to the big tv from an iPad. A good way for a few people to watch an evening Zoom presentation together on comfy seats. Almost like extremely local tv I guess!
Hope some of that helps.
PS … Remote Buddy will let you control a number of Apple Apps on the Mac Mini, Photos, Sound, Books, etc with the Harmony remote (Apple Remote too if you have one) I’ve not tried this myself, but may be what you are looking for?