> Referring to Richard Stallman as "Richard", Steve Jobs as "Steve" and Chris Lattern as "Chris" in the letter comes off as a bit sarcastic/snippy in tone
Not necessary. First names are often used for familiarity, and it is fine e.g. for celebrities. Although, I have no idea who is Chris :)
That's right for familiarity. Unless he personally knows each of them, he shouldn't assume such familiarity. At least where I'm from it's considered uncouth to do so. Of course it's a cultural thing, and perhaps where you're from it doesn't sound the same way to your ear.
I think it's more personal [opinion] thing rather than cultural. To me, "Mr. Stallman" would sound sarcastic. And don't forget that we're talking about celebrities. Another example - if you've grown up on Beatles music, you'd say Paul and Ringo rather than Mr. McCartney or Mr. Starkey, right? And I'm pretty sure Paul and Ringo prefer the former one ;)
Not necessary. First names are often used for familiarity, and it is fine e.g. for celebrities. Although, I have no idea who is Chris :)