Raspberry Pi 4 2GB

I mean the four gigabyte version is just nice to have, but if you're not planning on doing anything like desktop oriented, like you know, running load...

Uh, it doesn't seem to be anymore okay, so it definitely fixed the uh video problem. We just need that audio problem sorted out, uh we're definitely g...

You need a controller that manages your smart devices locally (on your network) and that means a computer managing those things. My personal favourite option for this is a raspberry pi 4 running homeassistant (checkout r/homeassistant). You can hook up all your stuff locally and if you have lights and switches that themselves don't rely on connecting to the internet (zigbee, bluetooth, zwave, etc...) then you're good to go. There are heaps of instructions for setup available in the homeassistant community and the forums are awesome for help there.