Hey there! This FAQ describes what can be typically reused if coming from a Vivint Sky panel. Unfortunately it’s not much.
If your door sensors are DW10, not DW11, they should work fine with a 345 Mhz IQ Panel 2+, available here.
The V520IR and V620PT are Alarm.com model cameras. It sounds like those were likely installed a while ago when they still used ADC for the back-end software.
If those cameras are no longer associated with an account they could be reused, but based on all experience of our other users, the old accounts are generally not closed and the cameras are left tied to an Alarm.com account unless you can go in and manually delete them. If you have access to the account still, login and visit the Video Settings area and video device info. Delete those cameras from the account if you want to use them on a new account.
Kwikset door locks can be reused, but must be cleared using the Sky Panel first.
The CT100 cannot be reused with Alarm.com as it has been discontinued for new accounts as of a couple years ago.
The DW21, SMK001, likely the carbon, and the Doorbell will not be compatible and would need replaced. The DW21 for example is a proprietary variant of the DW20R.
Alarm.com service does in fact integrate with Alexa, more so than Google Home, with more voice control options.