Hi delToro,
All of BM’s ‘R’ bikes share a similar ‘feel’, from having the boxer engine and telelever suspension, making them easy to ride and control, and they all are able to be equipped with heated grips, ABS (when new, but a lot of secondhand R bikes seem to be ABS-equipped), practical luggage, different screens etc. and they are very comfortable, and are designed for the pillion to enjoy all day too. All R bikes are fun to ride as well as being sensible, which is a great trick, as the two don't usually go together.
The roadster is a very different look and image, and I think is intended to appeal to riders who prefer the simplicity, compactness, and back-to-basics appeal of a naked bike. The ‘R’ is lower & smaller than the GS, but not actually all that much lighter. And although the GS looks huge, the wide bars and low centre of gravity make it easy to control at low speed. Just like the GS, the 1200 version of the R is much lighter than the 1150.
I’m a fan of the roadster, but the GS just ‘feels’ right for me. I like the roominess, road presence, the view from the seat, and the feeling of control from the wide bars. Why not try them both and see if one of them feels more right for you?
Something to think about if you choose an 1150 R, is that they were available with a choice of short or long (overdrive) 6th gear. The short gear gives more overtaking punch at high speed, and the overdrive gives more relaxed and economical motorway cruising. I think the 1150 GS has the overdrive 6th as standard, and probably the 1150 GS Adventure has the short top gear, but another GSer may confirm or correct this for me.
Re your second question, although roadsters are perfectly capable of long-distance touring, you mostly see them around town or out on Sunday, when you see them at all - they're not nearly as popular as GSs (in the UK anyway). I looked at quite a few roadsters before I bought my GS and they tended to have low miles comapred to GSs. Also BMW owners seem to be quite good about keeping service documentation, so you can check that. If you buy from a BMW dealer, the bike's history with any BMW dealer will be on computer.
I visited Norway on my GS and you are very lucky to live in such a beautiful country with such great biking roads, little traffic, and fantastic scenery. Whichever bike you choose I wish you very enjoyable riding.