I am not sure I got it exactly.
You buy the character of your player, then, the character is moved to a specific region, where certain magical items (that provide abilities) are sold. You have 30 seconds to buy them. After 30 seconds, you are moved to an arena type of region. When every monster is killed, the character returns to the shopping area, where he has additional 30 seconds to purchase stuff.
1) Are the monsters owned by Neutral Hostile?
2) When the monsters are killed and the character returns to the shopping area, will the monsters respawn in the arena?
3) Do you want it to support multiple players?
4) What will happen if the character is killed, while facing the monsters?