It sounds like at least two TVs are in the picture here right? Just correct me if I’m mistaken. If it’s more than 1 that affects my thinking. Because while it’s easy enough to set-up a system that directly connects to one television and if you only need 1 TV then an Nvidia Shield Pro that directly acts as both Plex Media server and the client (and has codec support for everything, it’s excellent, the only thing in the same category would be AppleTV devices).

I guess it would help to know what streaming devices if any you have and use for the current TVs.

I was toying around with the idea of a raspberry pi as a media server

Definitely not a bad idea in principle but currently they are either heavily back-ordered (I suspect you could end up waiting 6 months or more) or very expensive. Whereas once they were $40-$50 with a power supply, now lots of places are charging twice that.

that was also attached directly to my TV,

I’ve heard of this, I don’t know enough to say whether it’s a good idea. I think the last time I heard of this it was people using it for Libelec and/or Kodi installs. You’d need a remote as well so that increases the cost however much that costs ($20, guess you could also get a Bluetooth keyboard/mouse combo but about the same cost or more).

If that’s a mini pc Linux box with specialty fans I can go that route, but if there’s a simpler option it would be preferred

The Nvidia Shield Pro option is pretty simple with Plex (assuming you have streaming devices that can run it, hence my question above).

I get the impression that most modern video files are 4k, which needs transcoding. Is there much selection of classic h.264 files in 1080p?

I would not at all say that right now. I still see a ton of 1080p stuff, probably the majority in fact because you have encodes for it going back 10 years now. QxR (basically the last standing quality release group in public) does 1080p encodes alongside 4K ones for all their releases. When I look around I see more 1080p than 4k. For newer shows I can almost always find a 1080p rip of them alongside 4K (which may in fact come out later).

That said, it is something to keep in the back of your mind because the situation will not be the same forever. I would bet in 5 years there will be increasing cases where there aren’t 1080p releases. But I do think 1080p is going to linger longer than SD because the jump in quality is not as massive to most people.

Tons of stuff is still released in 264. Though 265/HEVC is now mature enough unless you really have stuff that can’t support it, there’s no reason not to go for quality 265/HEVC encodes as they can be slightly smaller and higher quality at the same size. (Just do go for good releasers, QxR for example, people who include mediainfos that show bitrates are at least 6-7000kbps for 1080p (though animation can be done well at half that as it compresses very well in many cases))

If you go for the <3GB/hour 4k 265 mini-encodes they’re of course going to look like garbage because of bitrate starving, go for the 3GB/hour and up 265 1080p encodes and you’ll enjoy them.

Go ahead and tell me about your device situation then I’ll give you my thoughts on some options, their costs and drawbacks.