KeePassXC and Keepass2Android auto-synced with my Nextcloud instance. Works great cross-platform for Linux/Windows/Android.
I know what you mean, trusting a SaaS provider with my master password list always felt like a bad plan.
Just the normal 2160p is probably what you want, remuxes are going to get very large with marginal benefit. You might have trouble if you're using the built-in smart tv app for plex, but the plex app on chromecast will keep up fine.