Oh, will Lich have to kill to survive? Well, based on that.
I would build a central stronghold, a dungeon of some sort, and several smaller hidey holes near enemy strongholds. Cities mostly.
Then I would attack the cities in order to get my needed kills, and retreat to my hidey holes. Moving randomly to new areas to throw off pursuit.
Once I was powerful enough, I would conquer the enemy ruler, surrender the kingdom to my own king, and move on to another enemy :-)
For this service, I would expect remuneration in my following lifetime.