Forum wise, http://www.totalmini.com/
is the place to start for an active community. Regional ones are everywhere, such as http://surreynewmini.forumotion.com/forum
The interior is a little low rent in comparison to the mainstream BMW offerings, but the Countryman is a bit better (newer) and has just had a refresh of the interior as well, though I haven't seen it.
The ride quality is better than an E90 on RFTs, and whilst not a true chuckable MINI it is still a fun little car to pilot down the road. Whilst it rolls a bit more being that much taller it is still streets ahead of something like the wallowy Yeti (another good car) for fun driving.
The Cooper / Cooper D are competent, and would be fine around town, but when you get out on the motorway they are a bit lacking in urge. The S and the SD address this deficiency, but are still not going to set the world alight, sprightly, but not quick.
Description of the 4WD system can be found here:
There have been conflicting reports of the torque split actually used. I think that it started with the 100% front and up to 50/50 as needed in the above article, but was then clarified by MINI to start at 50/50 and then reduced to full front drive as speed increased, unless extra traction was needed. In practice on tarmac there is little to differentiate the two in terms of driving characteristics as there really isn't enough of an excess of power to trouble anything but a total hooligan.
Space wise it has a lot of room for a little car. The rear seats can be adjusted for angle, and the rear seat bench can be slid fore and aft to optimise boot space / rear leg room. The driving position is a bit more upright than something like an X series BMW, but is similar to other cars of the class and you get used to it pretty quickly.
My Sister has had hers (Countryman SD 2WD) for about 18 months now and is still very happy with it. Only trouble so far has been the silver adhesive on the window trim coming off (known problem) and that was quickly fixed under warranty. She wanted a diesel, and driving the Dooper and the SD sold her on the SD for it's better out of town performance. 4WD on RFTs isn't going to help, so she saved the weight and money and runs winter tyres instead.
The pedal pressures are a little different, in that the clutch engages quite high on it's stroke, and the brake pedal is a little long in comparison to other cars. But as soon as you get your head around this it's fine. A few revs as you pull away and it pulls off fine, and the brakes give you great progression whilst still really pulling you up if you stamp on them.
The looks are a bit individual (hers has become known as the Dumpyman in the family), but is a great little car to drive. Get out there and test drive one!