i have a addictive personality
This isn't good...you WILL find yourself obsessed with online poker, your moods will be affected by how good of a day you had at the tables, etc. You have to learn to walk away and forget about poker for weeks if necessary.
How good should u be before u start playin real cash online
You should know some basic concepts of the game and learn how to play a tight-aggressive style.
I would deposit some $$$ into a site with a bonus (Party is a good one) and play at the low-level tables and gain some experience.
If you like nano-limit games, which are good to perfect your straight-up play without risking a lot of your bankroll, I would suggest PokerStars
. They have .02/.04 limit hold'em games as well as .01/.02 NL hold'em games.
Good luck starting...