Brandon,
That sounds reasonable. My method is quite similar, even to the use of SyncToy. (I don't do the online part, but substitute a second external backup drive which is just an occasional copy of the main backup.)
But.... I woke up one morning in a cold sweat; what if a folder in my image directory was accidentaly deleted ( don't care how at this point)? SyncToy would faithfully sync my backup drive and delete that same folder. EEK.
Since I autorun SyncToy everynight, that scared the cr@p out of me.
Since then, I auto run SyncToy in "Contribute" mode which replicates new files, changed files and renames. But it doesn't do any deletes on the backup side.
Gradually the source and backup will get slightly out of sync, as deletes accumulate on the source, without being replicated on the backup. Periodically then, I run a Full Sync between the two, with the preview option enabled, to satisfy myself that nothing unanticipated is going to happen.
Just a thought, YMMV