What hardware will be optimal for a server in a car?

Question

Iron

Good afternoon!
It is necessary to assemble a simple file washer to organize a media server in the car, so that there is something to brighten up a long road. The requirements are simple, but somewhat specific:
1. read- only data (no torrents), mostly movies and music
2. up to five clients watching movies at the same time (maximum FullHD, no high bitrate is expected to save space)
3. clients are tablets, the way sharing, most likely - samba
4. I don’t see a way to connect tablets by wire, so it’s wifi through a router connected to a file washer via gigabit ethernet
5. vibration resistance (i.e., at least data storage on ssd)
6. Work from 12V (although there are 220 in the car). There are a number of mini-STX and mini-ITX mothers or Barebon systems with DC input right away.
7. Minimum power.
8. Of course, you want something cheaper :)
9. [bonus] Appetite in general comes with eating, so system scalability is welcome. Say, what if it comes to mind to organize video surveillance of the perimeter of the car? But this is a low priority item.
Emerging questions:
1. Processor. A powerful one is clearly not needed here, but my knowledge is not enough to understand, but what kind is needed? Roughly speaking: celeron/atom, i3 or just i7? (Xeon is not considered, because here it’s like shooting sparrows from a cannon, and it eats a lot of energy.)
2. Memory. On the one hand, file cleaners don't need much, on the other hand, they can prefetch data from disk and still need some. How much?
3. As a router, I considered some piece of iron from Mikrotik (I love them) with built-in support for sim cards or support for an external 3g / 4g usb modem. The Internet is also needed on the road. Therefore, in fact, I did not consider the option of file cleaning with wifi: why, if a router is planned. But maybe it's all in vain and directly from the server and make a router?
4. OS? I would install Ubuntu Server, because I already worked with her somehow, but there may be other opinions. Like XigmaNas, OpenMediaVault, etc.
The purpose of the questions is to understand the boundaries of system requirements and then pick up the hardware. Maybe it will be a do-it-yourself kit, or maybe a ready-made barebon system. Thank you!

Answer 1

Do-it-yourself budget computer in the car .

Answer 2

Just NAS-s - not an option?

Answer 3

Mikrotik would be good to use since you love them, but the usb is rather weak there as people write. same with raspberries.
Orange Pi eats normally. dc-dc converter is also no problem to find it for you not atx. though one sata hole ...
I think Orange Pi will suit you.

Answer 4

If you want "seriously and for a long time", that is, Intel NUC , for example. This is a fairly productive piece of iron, plus inside it has a neon compartment for a 2.5 "drive, there is an M2.
If the NUC is not on the budget, then the Chinese have everything like this in the widest range.