>I heard you can get to be a guild leader by getting tons of
>gold. Can someone elaborate a little? What's the process and
>how much gold (ballpark) are we talking about?

Help Kingpin will get you started about the guild leaders. Ultimately, you get to be a leader by winning a "Vote". A vote for leadership may be called by someone who is an elite member of the guild, and everyone who is elite may cast a vote for someone. In the case of a tie, whoever has the most donations wins. As to how to donate to the guild, help guild join should explain most of that.

Typically, Galadon, Hamsah Mu'tazz, and occassionally Voralian City are the only three major thieves' guilds that have much if any activity. Often, if no-one is the leader of Dagdan or Blackclaw, you can become elite, call a vote, and win by default.

>Also, is that gold that's in the bank or do you have to make
>donations somehow in the guild? I haven't see a way to do so.

As above, it should be rather well detailed in the "Help Guild Join"

>Are there any benefits to being a guild leader other than the
>title and general badass factor?

There's two or three "handy" skills you get, but I forget what they are offhand.