[RyderX]

Answers:

1.There isn't any difference between pickup; and pickup[MAX_PLAYERS];.
2.Just under public OnPlayerPickupPickUp(playerid, pickupid), add this function DestroyPickup(pickup);

For example:

public OnPlayerPickupPickUp(playerid, pickupid)
{
if(pickupid == pickup)
{
SendClientMessage(playerid, -1, "JAJA ITS A PICKUP");
DestroyPickup(pickup);
}
return 1;
}