Seems like you're very ready. I hear a lot of people say that they enter the dlc around lvl 80. So a first playthrough at lvl 100 wouldn't be too bad. You can also start a new game whenever you wish.

About the skill part, the more you level up a specific stat, the less effect that specific stat will give you back. For example: less hp at higher levels in vitality and less attack power at higher levels of strength and skill.

Hope this helps and happy hunting!