I have a smart home and let me give you some advice. BE MINDFUL OF THE BRANDS YOU CHOOSE. For example, using tuya smart devices with home assistant is a pain, you have to setup a tuya cloud account and get an API key that you'll have to renew every few months. If the device gets reset you have to go back into the cloud environment and re-add them. It's such a pain. Almost anything works with home assistant, but the amount of diy and bullshit you have to deal with to get something working varies greatly between brands. I highly recommend sonoff, also get a zigabee controller for home assistant as its far better than using WiFi. I also recommend you start a notion document or some other form of document that can keep up with everything for you. What brand of switches are in what room, what brand of lights are where, etc. Not just for you but if you ever sell your home you can give it to the next guy. Because you're probably not going to take the light switches or any in line relays with you.
Also to not connect to the internet you need to have a separate network (router or access point) that all your smart devices connect to. You'll then use a VPN to connect to your home network remotely. Basically have your smart devices router hooked into your normal router and on your normal router block external traffic (the Internet) from going to the smart devices router. Sorry if that's hard to follow but just Google "how to segment a home network" and that should get you started. Feel free to hmu if you need some guidance.