I'll do my best.
A) Yes, though his brother Zack also helps with design, as do (I think) a number of older, long-term donators. That last part is only my suspicion though, because Toady refers to testers helping him with the alpha but won't answer any communication from me about that stuff.
B) I think Footy is just a forum\bugtracker helper, though he may be helping with the aforementioned stuff.
C) Toady's brother has or had a day job, at least last time I read. The donation totals are posted by Toady in the dev log each month.
D) There are 50 possible reasons, but the most obvious and immediate is that once you do, other people fork your code beyond recognition and you run the risk of losing control of your project to a more popular fork. That would not be fair to Toady since this is his livelihood.
E) Do those people really have any way of forcing anyone to do anything? My conclusion there is "no". In that sense, keeping them at bay is just as easy as not caring how rabid they become.
Welcome to the forums, have fun, and don't pay any attention to the few extremely vocal and often mean people that are somehow not banned from here. Nearly everyone here is really cool, otherwise
Also, since you're new, here are some essential websites.
http://df.magmawiki.com/index.php/Main_Page <- DF Wiki.
http://www.mkv25.net/dfma/ <- Dwarf Fortress Map Archive. Hosts an excellent Flash applet by Markavian that lets you compress, upload, and share your forts online, adding map notes and much more.
http://bay12games.com/dwarves/ <- Dev log. At the end of each month, Toady stops working on Dwarf Fortress proper and spends a number of days equal to the number of weekend days in that month, working on a "secret project" of which we know nothing. Don't bother asking about it