Yes, you can probably manage your system so that it is not using the HDD for swap files but you will spend more time opening and closing applications.
Depends what you're doing. Mostly I'm running some combination of email client, accounts package, Office applications, web browsers, and C++ IDEs and applications, and that lot rarely comes to as much as 2G.
On the other hand if you're in the habit of for example running Java applications, particularly if they use Swing, or doing video editing, then you're likely to benefit from all the memory you can add. (Or getting the Java stuff rewritten in a proper language, but that's a different argument.)