This is the setup I'm using, too. Does everyone have the irritating problem on Windows, though, where Synctrayzor really likes to float some sort of tooltip with its own name in the upper-left corner? Even overlays full-screen games for me.
Same. The free version is sufficient. I use it to transfer the full resolution photos and videos from the phone to two computers. Syncthing is also good.
I don't do Windows, but I happily sync directories between my Android phones and my Linux PCs (especially a cloud server I lease) with rsync over ssh within Termux.
If you can set up an rsync server on Windows that should work. Besides actually implementing robust and efficient sync, rsync is also smart about platform differences.
For the specific case of Windows to Android, I've heard of people scripting up tools to shove all the contents of a directory over adb push.