@Sebastian: correct, the chaos of my list of bugs is already manifesting in my thought process.
@Machtnix: If there is 'download needed' press build, it will download it automatically.
We only provide the most prevalent architectures for the platforms to export to (because building is a lot of work). It is recommended to always use a 64bit Linux and if you're using 64bit Linux and our player is 32bit you will get hella trouble. Steam won't even distribute the 32bit version anymore. The engine also doesn't profit from 64bit architectures, it's only about compatibility. So the architectures are as such:
Windows: 32bit
Mac: 64bit
Linux: 64bit
Windows is in 32bits because that is the best compatibilty option. The player supports from XP to 10 nearly every PC.
If it's 32bit or 64bit is completely irrelevant for your game.