Another vote for home assistant. It is not just the best FOSS option, it might just be the best option altogether.

Some advice, think carefully about what you want to achieve with automation before you start. Take some time to draw up what you are going to do before you buy anything. Think about extensibility and don’t force yourself to lay out big money and time all at once. Will Smith (tested.com, tech pod, not Independence Day) recommends doing one room at a time and focusing on spaces that are primarily yours first.

Things to consider: If you live with other people, it might be wise to make everything transparent. Meaning the light switches still turn the lights on and off on demand etc.

Wi-Fi is sort of a poor solution to communicating with devices, especially ones that don’t have access to mains power all the time. Consider if you are going to deploy zigbee, z-wave, or a matter mesh. Matter, being very new would be challenging but it is clearly the future of low power wireless communication for home automation.

Set a goal that NOTHING requires a external service or internet connection and stick to it. That might mean giving up on some types of devices but it’s YOUR house, not google’s.

Think automation first. Phone and voice control is cool. But having things just happen the way you would want without have to do anything is even cooler. Be smart about complexity though. How would things have to change if your partner started working a different schedule for instance?

Finally, get creative. Lots of silly problems can be solved with this technology. My favorite automation turns the damn hot glue gun off after 30min so my kids don’t start a fire if they get forgetful after a craft project.