1) The FSDT Universal Installer needs to be a clearly defined utility (with a clearly defined .exe) that simply launches without updating anything. Currently I think its using some sort of command for the Couatl updater: "C:\Program Files (x86)\Addon Manager\Couatl_Updater.exe" /SILENT /INSTALLMODE=TRUE
That's functionally equivalent as being a separate .exe, without having to have two separate .exe doing the same thing, just with a different interface. If you follow the instructions and always use the Shortcuts to star the installer or the updater, they *are* like "clearly defined" separate utilities.
2) The Universal Installer itself needs to have its own version number clearly visible somewhere, and an update button next to it when a new version is available.
Not required, since when you start it from the Shortcut, it will UPDATE ITSELF, if needed, so there's no need to an update button or a notification or a version number, because starting from proper shortcut will end up with the latest installer start, no matter what.
3) Next to each piece of software, like GSX and airports, it should mention the version installed, and the latest version number of the software available
Having version numbers will only give you a false sense of security. What's a "version" for a scenery that might be made of thousands of files ? How we can be sure that, even if the program thinks you have the right version, some of your files might still be outdated ?
The only sure way is checking all files one by one, yours against the remote, and this is what takes longer and this is what is done when you press "Update", which really means "Check for updates and download them", but that wouldn't fit a button.
Because, if we tried to "cheat", by showing you a version number taken by, for example, from the manifest.json file, and we disabled the "Update" button if your "version" is "correct", you'll get a false sense of security that ALL your files are the latest version ( which is impossible to know, without checking them, one by one ), so you'd miss important updates.