Oh and one more thing that trips people up: iCloud is not a backup. If you delete something from your phone it will immediately be deleted from iCloud too. The phone will even sometimes stealthy delete the local copy of music, photos, etc to save space and silently re-fetch them as-needed.
“iCloud Backup” is a thing. It backs up your configuration and some other things in case you need to factory reset or buy a new phone, but that’s separate from iCloud data storage.
Speaking of iCloud Backup, if you’re concerned about privacy don’t use it. Sync your phone with a pc instead and choose the encrypted backup option.
In my experience, if you want to use smart home stuff you really need a hub of some sort rather than connecting everything directly to your phone.
Smarthings is popular, or Hubitat for the more tech-savvy. Or just an old PC with HomeAssistant or OpenHAB installed. All have ways to expose their connected devices to HomeKit/Siri.
If you go the old PC route, just make sure not to buy any ZigBee or zWave devices since they’d need additional antenna dongles (built in to the standalone hubs) to function.