re: Poker & whats the average size for a tourny?
The major difference is in the time that the tournament will last.
If you join one that large, you can expect it to take 4 hours to get to the Final Table. May be more, depending on the blind structure at the site in question.
So, don`t play in a big one unless you have plenty of time available. You need to be well rested and alert too. No point in entering a tourney if you are going to be half asleep and unable to play well by the time you reach the late stages - voice of experience, I regret to say.