I've been on two cruises, both P&O and both to Norway. Went on Arcadia first time and Iona second time. Personally I think it's one of the easiest holidays I've ever had. No worries about finding places to eat as it's all on the ship (unless you want to sample local delicacies)! Not had any issues so far (other than the websites, cruise companies cannot build websites that work well), and it's relaxing. Best bit is that the hotel moves with you, so you don't need to repack and unpack when moving between places, that all happens while you snooze in your bed.
I'd recommend it. Drinks package is something I've never done as I don't touch alcohol, but to me it seems to be of no value unless you are going to be drinking dawn til dusk.
I would always recommend a balcony cabin. Sitting and just staring at the vast expanse of blue is great.
With regards to internet, the broadband deals on cruise ships are pricey! Just enjoy the digital detox, unless you have free roaming charges to your destination (which I found out I did), then just use it to satisfy curiosities on shore.
Best deals? No idea, it's expensive, but you sometimes get discounts for being a regular. But from experience booking earlier is better value than last minute.