Neil Gaiman is on Tumblr, and is very active there. Also one of the only celebrities whose presence is actually enjoyed, not merely tolerated. Also present are Diane Duane and Peter Morwood, and likely several others I haven't found yet. They all interact with followers and fans alike, and are happy to receive messages about their works.

This is not a hard-and-fast rule, but rather a general guide: most creators are happy to receive fanmail by any means, hand-written, typed, electronic, you name it. Just don't be weird or creepy.

Yes and no. Deaths in the US are exceedingly rare, but it's only because of how seriously we take rabies here. If you are infected and do not receive treatment before symptoms manifest, it is 100% fatal.

The good thing is that it is pretty easy to avoid rabies exposure in the US. Just maintain a safe distance from wild animals, as you should in any case.