I wouldn't recommend running every day. My body has too many aches and pains, especially my feet. I have to give them time to heal. Plus I dont want to get burned out. I just finished week 4 and look forward to my runs, hope it stays that way. Week 5 I'm afraid is gonna be tough. But like you I enjoy the challenge. So far I've finished every one, and as far as the biggest challenge? It's been mind over body. My mind says you can't make it every time I run, so I have an argument with it each time. So far I have won each time, hope it stays that way.