If the seller still has it, you could ask him to set it to 31KHz before he ships it. Then you'd just need to to plug in the VGA adaptor and you'd be ready to go.
Don't mean to sound patronizing, but if you're new to the Amiga, you might not know that you should NEVER unplug anything while the power is on. So just be sure to power down before swapping cables in getting your machine set up.
Enjoy your 4000 :-)
