First, let's tackle your query:
When I say "email" I mean just enter the word "email" without quotes-- not the address or anything. Just the word! :-)
For the hidden fields, a fellow user, Steve Willats, made a tutorial for aweber: http://www.brandonkraft.com/uploads/enews-aweber-draft.pdf
He includes screenshots and is very step-by-step.
Regarding getting it to look better, do you the StudioPress forums and ticket system to ask for help!
To address rohanpawale's issue, yes, you don't need a plugin for this. The real advantage of this plugin is for people who bought a theme from StudioPress, such as Streamline, which I'm using on my own site, and want to make the subscribe form look like the great one that Rafal designed for that theme.
Instead of asking a novice user to edit HTML and CSS, this plugin allows you to quickly take advantage of that built-in styling.
As far as performance, you do want to limit your plugins. I'd venture that the vast majority of plugins are needed if you know what you're doing in HTML, CSS, PHP, etc. The advantage of the WordPress platform is for anyone at any skill level to be able to install and run a website. This plugin does cater to the technically novice user category.
WordPress 3.4.2 has 981 files. Adding one relatively small php file and the associated readme won't have an impact on performance.
If you need additional fields (first/last name, etc), please let me know. The code is ready for that but does require a little CSS to make those fields look good.