Naw man. You should join ISBoxer Discord (
https://discord.gg/ESxEzhs), we have a #wow_classic channel and a bunch of people chatting away in it 24/7 including lots of people who have successfully done what you're trying to do!
But here's what you can do to solve your problem:
1.
Grab the current Inner Space development build. A new detection has been added to Inner Space (in the dev build) that should automatically add a
"World of Warcraft Classic Client" Game Profile to your WoW game in Inner Space. To get that, right click Inner Space and select Patcher, tick "Download development (test) patches" and then close and restart Inner Space for it to pick up the test patch info. When it restarts, it should pop up the patcher window with a list of files it says are available, and you will need to click "Patch these files" for it to actually patch.
1a. Alternative to #1. You don't
need the development build of Inner Space. You can literally just use Add Game, and point it at the wow.exe in your WoW\_classic_ folder, and just pick your added Game/Game Profile in #2 instead of the new automatic one.
2. After this, all you have to do is select the "World of Warcraft Classic Client" Game Profile (or the one you created in #1a) for the Characters in ISBoxer that you want to launch classic. If you're using the Quick Setup Wizard, you will want to manually select this Game Profile from the drop-down on the Characters page. If you've already used the wizard, then select each Character in the top left pane, and check the Game/Game Profile drop-downs in the bottom right.
That's really all there is to it.