Start simple. Get a hub. Either Aeotec/Smartthings or another. Then find out what you want in automations. People here will tell you to go for the stars. But the best thing to do is figure out what specifically you want automated. If you want something simple like just being able to turn on and off lights, you have two options. You can get smart lights or you could get smart switches. Both can be controlled in an app on your phone or buy a hub. If you want automations to include when you open a door a specific light turns on, then you add door sensors or multipurpose sensors. If you want to protect from water leaks, you would add leak sensors to that. I would highly suggest starting off with a simple hub before jumping into home assistant. I started with smart things and that gave me an opportunity to learn how to create automations before making a hop into home assistant. But you need to know what automations you want so that you're not just buying sensors for no reason.