How “big” are your movies and tv shows? If they are 4k UHD remuxes then Nvidia Shield Pro or Apple TV 4k behind a firewall to block external internet is your best option for performance, usability, and privacy. You will want to ocassionally allow it internet for software updates. Kodi, a mini pc, raspberry pi, etc. would be more private but you trade off a seamless remote, easy interface, and streaming codecs (e.g., dolby vision).

The pine64 Pinecil is a great starter soldering iron.

You’ve already received some great suggestions. Another one is Netdata. Personally, I use glances to collect the data and Home Assistant to display the dashboard. But I only do this because I already had Home Assistant running.

Latency tested using librespeed.org is about 50 ms.