dont: Used HDD are not worth the risk/cost as the chance of failure outside of warranty is too high. Maybe: Enterprise SSD’s, sometimes you can find low ware SSDs that are cast off from enterprise organizations at reasonable prices, often more so if its used SAS as average consumers need an HBA to utilize the drive. Be cautious as some SSD’s are discarded because of firmware bugs that cause early failures.
WiFi sucks for cameras when possible you should always run a POE camera for both power and data.
I also always suggest avoiding app subscriptions because then the period of support is out of your control and they can cut you off from an otherwise working camera and you have no recourse.