Bumping this up!

My company has a fairly inexpensive Biz class fare on UA EWR-IAD-EZE and I'm thinking about going down right after Xmas for a couple of days. A couple of questions:
1-is a visa necessary
2-given the problems earlier this year, am I insane as a woman travelling solo to BA
3-chosing between Hyatt & Starwood (I'll only be there 3 nights)-- which should I go for (I'm top tier in both).
4-I have minimal spanish speaking ability--but am willing to try, will I be ok within the city itself?
5-What's good to buy (not too expensive).

And last but not least, will there be any other FT'er in town Dec 27-30???