SimonLovskog

If you decide to use those kinds of adapters, be really careful. If you draw more power than their rating, your computer can potentially become a fire hazard. I would rather get a new PSU if you can afford it.

Generally, the alternatives to Plex are Emby and Jellyfin. Jellyfin is an open source fork of Emby. The main differences between Emby and Jellyfin is their client support, and of course Emby has a paid service for certain features. I used Emby for a couple of years before switching to Plex. My main reason for switching is how much more polished Plex's UI is. This is especially apparent on certain devices like the Apple TV and mobile devices. However, Emby UI is in no way bad, I just like how polished Plex's UI is. Basically, If you don't really believe my UI argument, use Emby, and if you don't want to pay for certain features and are okay with lacking device support use Jellyfin.

Upgrading CPUs in laptops often isn't possible, do your research and check if you can upgrade the CPU in your laptop. Upgrading ram, and storage is however probably possible. Btw, it is probably DDR4.

Hardware looks fine, Ryzen likes higher frequency memory, but I have no idea if it matters in this environment. You could also get an Supermirco Atom board. It offers some more SATA ports, via the SAS ports. Also has IPMI, and other server features. If you want some hardware decoding for plex, get a Nvidia Quadro P2000. If you like a simple and safe experience go with Unraid. Another choice could be to just run Ubuntu Server, ZFS, and docker on top of it.

I use Autodesk Fusion 360, its free for Students, and Hobbyists.

If you want hardware decoding, and no gpu you need an Intel CPU with quicksync, btw :).

I have got an Nvidia Quadro P2000 in my machine, it flawlessly transcodes 4K HEVC streams. Single slot, and no extra power.