@xoagray @AmarettoBear Yup. The most difficult part is actually installing physical light/fan switches and finding which ones you want, and thinking about sensors, time/days, proximity (your app), etc. as inputs, and switches/smart bulbs, etc. as outputs and how you want the automations to work.
Home Assistant can easily be installed in an older HP Mini system (think Gen 7-8 Intel) with 4-8GB of RAM and a 256GB SSD and an Aeotec Z-Stick 7 for ZWave and/or a Sonoff Zigbee 3.0 USB Dongle Plus for Zigbee devices.
Though I personally recommend starting out with a hubitat for local devices, and playing with a Home Assistant later. It works with just about everything - Zigbee, ZWave, Matter, etc.
There are communities out there with a wealth of knowledge.
I've done things like integrate with the third party Litter Robot API so that when @hypoidbear 's kitties poop, it reads the status change, and then turns on his laundry room vent for about 5 minutes after the litter robot timer goes off so it's less stinky in there. That's a cloud-enabled smart device's status change enabling the changing of a local device's status for X time.