Mainly, I don't want to be obnoxious and friend 15 people in one day, but how will people finally know I'm in facebook unless I friend them?
Facebook puts limits on how many friends you can ask for in one day--they will send you a warning message if you are adding too many. Not sure how adding several when you start is obnoxious though--people expect others to add several people right at once when they start.
To answer your question:
They will see your name if you friend a mutual friend/relative;
They can find you if you've entered your high school and/or college and they go to search their year of that school (unless, like me, your high school no longer exists...FB has no way yet to list non-extant schools!);
if THEIR friend finder is working (mine does not--Facebook glitch), they can enter their email address and see whom among their contacts has recently joined FB, including you!
To tell you the truth, though, I'm usually quite flattered if someone that I know (even distantly) asks to be friends...if I see someone I know friending everyone but
me, it makes me wonder! I don't think it's obnoxious for you to ask (although I understand the introverted thing, believe me).
As you've probably gathered, there's no set amount of activity that is normal...true friends will start to get used to your pattern of activity. I have friends who are always active, friends who are rarely active, and friends who cycle in and out of activity.