oh, thought you meant the 2GB would only apply to .msi and that "Inno Setup" would just need to be below 4GB (was assuming something along the lines of "Inno Setup" beeing in 32bit, thus creating the famous 2³² limit), was a missunderstanding on my behalf.
Yeah, the 7Zip based solution could handle files far bigger, only problem is, it is not capable of executing anything else. That would lead to a problem as currently I'm unable to create an installer which isn't dependend on some "regfiles", to get VBox to work.
So, my idea would be the following: Let's have to seperate installers, which only appear as one. So, the user doesn't see that we first use "Inno Setup" to install VBox, then load the SFX to extract the Gateway and Workstation (this way, "Inno Setup" wouldn't have to deal with larger files but only have to point to a certain path and run the .exe) and then let "Inno Setup" take over again, integrating the just extracted Gateway and Workstation VHDDs. This would of course in conclusion force us away from just having a .exe to necessitating a folder which contains all the needed files/installers.
So, here is what would happen technically wise:
1.) The user clicks on "setup.exe" to start the installer.
2.) The installer starts and looks for an already installed version of VBox.
2a.) If one is found, continue to step 3.
2b.) If not, proceed to install VBox in its entirety including the files needed for NAT.
3.) Without showing the user, start the SFX, point it to the folder where the installation of VBox was found (from now on this will be folder / to make it simpler), and let the Gateway and Workstation VHDDs (just to explain, these are NOT .ova's but already configured virtual HDDs) be extracted in /Whonix.
4.) After the SFX has finished extracting the VHDDs, run a script whose only job it is to create two virtual machines in VBox and link them to the VHDDs.
Just to explain, the reason I choose using VHDDs rather then .ovas which could be imported is speed. Adding a VHDD takes a few seconds, importing an appliance takes a lot longer. Furthermore, when adding an appliance, we'd have to remove these files again, something not necessary, when using VHDDs.
Have a nice day,