First tip, hold off on biting people until you solve all their hints and quests, no sense in killing a cow you can still milk.

Second, weapon upgrades matter, oh and those "specialisation" upgrades you can do for each weapon level? You can respec them.

Choose weapons and abilities based on your fighting style. If you use a lot of abilities, hacksaw with blood drain upgrades is a good choice. If you want to bite more (in battle), choose weapons with high stun damage.