The first thing you should do is get a dedicated server for your plex server software. I recommend the NVidia Shield Pro as your first Plex server host because it has excellent hardware transcoding capabilities. If you don’t want to buy the shield, you could get a larger server with a processor that has integrated graphics capabilities. Installing plex on that will actually give you a few more features and probably better transcoding capabilities, but it would be significantly more expensive.
After that, I’d get a Plex pass to unlock a lot of the good Plex features.