1. Yes, I know that Steam applications usualy have various issues/limitations. It happened to me I tried GM:S Free that had a compiling issue (pretty serious problem) and I and other users could not roll back to an older version and had to wait 1-2 weeks for the fix. As a workaround, the Steam users can now receive a standalone key if they want (still the layout editor is a mess, the interface looks like win98/dos, still has some bugs and the worst of all: the comunity is very agresive, if you point something about the issues you get downvotes or worst)
Long story short: So the Steam version does not have any advantage over the standalone version, only disadvantages.
2. Ok, then I will use my live.com mail.
3. Still not sure 100% what it means, but I will let it unchecked since I don't have any official business (at lest not yet).
4. Well... at least I tried <img src="smileys/smiley4.gif" border="0" align="middle" />