Void rangers can get away with not doing any quests except for maybe veng at higher levels. If you're looking to make a "perfect" void ranger or want to leave the possibility of transitioning into a zerker later down the line, just follow a guide for a zerker and stop at 42 defence (here, I wouldn't recommend doing holy grail, even though some guides recommend it). You only need to be careful about your def level as there's more leeway for attack and strength depending on how high your range is (attack and strength combined can be equal to 1.5*range before they start giving you extra combat levels).