flashfacts - Welcome! Good luck with your first week! I too run outside and not on a treadmill, for a number of reasons. Last year I was running on a treadmill- ended up with a stress fracture. This time around, running outside, because I'm going up hills, inclines and declines, I've managed to avoid the same thing happening again. Apparently running outside is good for your balance and bone density. Treadmills eliminate the bodies need to balance itself, and absorbs some of the impact of running (impact is good for bone density which is good in preventing osteoporosis!). This is all according to my GP btw, so don't take this as gospel.
Besides, those inclines and declines work different muscles. Which should result in some pretty nice legs

But like aka8941 said, it's about whatever you're comfortable with! You'll be surprised at how fast your body is going to get used to those inclines and declines!
aka8941 - W6D2 gave me the worst chest pains. Not like heart attacks pains, but I felt like I had been working my upper body, not my lower. Yay for pushing through! Good luck W6D3!!
I'm supposed to be doing week 8 at the moment, but we've been having really hot weather. Our mild spring has turned into summer with humidity, blazing sun and hot winds! So I haven't run 28 minutes yet. I got close yesterday, around 25 minutes, but I only got 15 minutes into today before I had to stop. I was so hot!
What a bizarre realisation I had tho - the idea that I was stopping running not because my legs were hurting or I couldn't get breath, but because my insides were melting and my skin burning from the sun.