1) the ones I have seen are around level 60, but there are the occasional high levels who can cast teleblock on you 2) make sure to bring an antipoison and some food if your defence is only 1. Since a lot of the pkers use dragon dagger superpoisoned. 3) i'm pretty sure the higher your level, the less chance for you to fail the obstacle, whether it is agility, mining, or woodcutting