As much as I think the Mini is one of the greatest cars on the road I would not recomend it as the "main" family car.
My wife had a Saturn L series mid-size sedan (almost the size of your Impala) and loved it but even that midsize car was getting tight with only one child, stoller, bags full of diapers, clothes and toys. The biggest pain is having a car that sits low to the ground and having to have to bend and drop into the seat while grasping/holding on to your baby and not banging their head (or yours) while doing it.
After having the Saturn sedan for over 2 years we decided to sell it for a 2003 Saturn Vue. My wife loves the Saturn Vue because it drives and handles better then the L-seies sedan (which ironically the Vue is built on the same chassis)even though the Vue is a car based small SUV. The best thing my wife loves about the Vue is that it sits higher then a sedan (but not as high as a big 4x4 SUV) and it makes getting our little son in and out of the VUE easier then any low sitting sedan or coupe.
I also thought that a coupe would be fine since I didnt really didnt want to even buy the sedan 2 years ago but its easy to underestimate how much space you need just for one baby/child. At times I even wonder if the Saturn Vue will be big enough when the 2nd child comes but my wife and I didnt want to buy a big gas-guzzeling truck-based SUV thats no fun to drive either.
Saturn enthusiast site -
www.saturnfans.com
Corporate site -
www.saturn.com