The secret about the $20 buy in is this...
Suppose you have 4 people, you take everyones $20, and split the chips in to 4 equal amounts. Everyone has lots of chips and you dont have to worry about chips being worth $0.05 or $0.10..they can still be worth the fictional 10,20,50,100,1000,5000 ...works beautiful and allow for a lot more action as everyone has more chips.