Well as the proud owner of a 12 month old and 4 pushchairs, I think I'm qualified to give advice!
For the newborn, they need to lay flat. We started with a Graco travel system. The great advantage of this is that the Autobaby car seat could unclip from the base in the car and clip straight onto the pram. This really is worth a lot. No need to disturb baby if they're asleep and no hassle re-fitting car seats all the time. We then bought a 3-wheeled graco pushchair - bigger pneumatic tyres but fixed wheels for off road. I liked the 3 wheeler, my wife preferred the 4-wheeled stroller.
At the young age, if you want to carry them with a papoose type thing, it'll have to be on your front. I didn't like it, my wife did.
Then, when they're bigger, we wanted a smaller buggy. We bought a cheap one from Kiddicare and it was crap. Handles too short and uncomfortable to push. We've just bought a Maclaren off Ebay and it's great, but it's only for town, not off road.
The best thing we bought was a Vau De rucsac carrier. I asked for advice on here actually, pretty much as you are. The model we've got is Swing. It was comfiest.
So in conclusion. Everyone has a different opinion. Yours will differ to your wife's/girlfriend's probably. Try and read reviews from places like Mumsnet before committing to buy and try them out first. For "outdoors" the rucsac's far better than a buggy IMO.
If you can, think about how soon you'll be out and about and how old your child will be by then. 7 weeks is November I guess - will you be waiting until Spring?
Evan at 6 months.