I would say number 5 was the only one I had never thought of. Too large for the installer. Interesting. All the rest seem like standard things to deal with, and I would assume many of them might have already come up just within the team itself. 32-bit and 64-bit OS's, etc.

Although I also didn't think much about having both steam and standard versions instealled at the same time. Is there that much difference? Couldn't you just do a system check for steam, if its installed ask the player if they want to install to their steam version. If 'Yes' then install via the steam path if 'No' then install normally. I am sure I have seen a mod do that already for me.

Otherwise, nice. I really liked the previous Stelae so this is a blast from the past!