Here's a quick "easy challenges" mod. Just put it with your executable for the game. Most things now only require 1 kill, or much less time. Activities now only need to gold 1 out of 3 or however many to get the challenge.
The achievements should unlock, I ended up using this near the end of my challenge list to get some challenges done and still got the achievement. I'd suggest editing the xtbl with notepad and making your own personal goals for each challenge.Will this affect Steam achievements..?