Which backup method?

Are your questions specifically about ReadyDR, or in general.  The answers are different depending on the backup method.

For other than ReadyDR:

1. If the backed up device initiates the backup (a "push" backup, it starts by making a snapshot.  If the backup device initiates it (a "pull), then it doesn't.  But if the backup device is on a power schedule, a pull generally works better.  So, choose your poison.
2. The "Windows" backup uses time stamps.  Rsync is standard Linux rsync (so will work talking to your new NAS when you get it, assuming it's based on Linux), which uses it's own "quick check" algorithm.  You can Google for more details.
3. No, it does not do a verification.
4. Clearly refers to ReadyDR only.

For ReadyDR:

1. Ready DR only backs up snapshots.  And it doesn't make one on it's own, it uses your most recent one(s).  Keep that in mind when scheduling snapshots and backups.  It's Netgear's implementation of BTRFS send/receive.
2. It backs up as many snapshots as you tell it to.  You can have hourly snapshots and daily ReadyDR backups, and all new hourly snapshots will be backed up.  They are snapshots just like on the source system.  Where data isn't changed, each points to the same data.  It can keep them for longer or shorter than you have your main NAS set to do.
3. No verification beyond metadata safeguards built into BTRFS.
4. It's especially more efficient on some types of files.  As an example, I use it to back up my Veracrypt files.  Using rsync, a small change in the file will cause an entire new file to be backed up with rsync or Windows backup.  ReadyDR backs up only the changed data clusters.  Given one of them is approaching 1TB in size, that's a huge savings in time and backup space.  This holds true for any type of file where file changes don't move all the other data.  Databases are another specific place where it can help a lot, though I don't have any of any size where that's consequential.
5. A ReadyDR backup is not a usable share as it exists, as it is only a set of read-only snapshots (and must remain read-only).  To create a usable share, you need to "clone" it (just as with a snapshot on the source machine).  On the plus side, it being just snapshots is added protection against unitentional deletion and ransomware.  Likewise, the snapshots on the sending system must be read-only, so you cannot have "allow windows access" enabled (which, IMHO, is a really bad idea in all cases).  You can have "Allow Access to Windows Previous Versions" enabled, as Windows treats those as read-only.

I use a pull rsync backup initiated by my backup NAS for all shares except the one containing the VeraCrypt volumes.  But I have some pretty fixed "down time" where nothing should be changing on the primary NAS  I have a share just for the VeraCrypt files (and also because VeraCrypt slows to a crawl on writes if Strict Sync is enabled, so I've disabled it for that share).