First, I'm dead jealous of you going to Iceland. If I could afford it, here's what I would take.
I'd take the Hasselblad and get the 50mm lens you are thinking of. I know this may be an unpopular view, but I can't see why you would take landscape shots in Iceland with a Leica if you already have a Hasselblad with you. You don't really need quicker handling in this scenario as the landscape isn't going anywhere (except very slowly down to the sea) and I assume you will be using a tripod. The bigger negative of medium format, combined with those excellent Carl Zeiss lenses, will provide far greater possibilities for producing big prints than any 35mm system.
With regards to film choice, it is true that Velvia is capable of producing stunning images, but for every great portfolio on Velvia produced by an experienced photographer, you can also find ten portfolios on Velvia with blocked out shadows or burnt highlights because of the limited dynamic range. After you've spent thousands on your Iceland trip, do you really want to come back with sub-standard images ? So only take Velvia if you are already absolutely comfortable with metering for it and aware of its limitations.
I definitely recommend Portra 160 as the choice of colour film; consistent and natural colours which you can adjust with more or less saturation as you desire in post-processing. Ektar can produce great colours on some shots then on the same roll, produce some awful colours which are difficult to adjust.
For black and white, I'm a bit less opinionated
. I think you should be able to manage with just an ISO100 film assuming you will be using a tripod. My choice would be TMax 100 but anything which doesn't scratch easily or curl should be fine - so stick with Kodak, Ilford, or Fuji.
Have a great time !