OP:
If you don't want to jeopardize the apps you have installed, I'd suggest this.
You'll need an EXTERNAL USB drive.
Download the High Sierra installer, but DON'T run it (on your internal drive).
Instead, choose to do an install of HS onto your EXTERNAL drive.
After the install, you will be placed into the setup app.
Begin setup, and when setup assistant asks if you wish to migrate data from another drive, "aim it" at the INTERNAL drive.
Setup assistant will "migrate your stuff" from the internal to the external drive.
NOW...
You can boot and run from the external drive "in test mode".
Without disturbing the current installation on your internal drive.
You can check each application, etc. -- to see if it works as expected with High Sierra.
When you're satisfied, you can then install HS onto your INTERNAL drive.
By the way, I STRONGLY SUGGEST that you create a USB flashdrive installer for High Sierra (instead of just "installing from the download").
You'll need a USB flashdrive 8gb or 16gb, and the free app "Boot Buddy":
Boot Buddy – sqwarq
With BB, it takes only a few clicks of the mouse to create the flashdrive installer.
Then boot from the flash drive and do your installs that way.