Option 1 does work but laptops are not ideal as a server. They lack the IO and have tiny heatsinks that tend to get clogged with dust. And those USB DAS are kinda expensive. And USB is less reliable than SATA although it usually works well enough for something non critical like a media server.
Option 2 is kinda bad as this NAS is too low end to run Plex. You need something with an Intel CPU.
You can get a used desktop PC for $1-200 that has a 6th Gen Intel 4 core CPU or newer and is able to house 4 drives or more. Only needs a bit more of power than option 1 or 2 but is cheap and works rather well as a NAS and server.