Jefe Bergenstein
Legend
Here's a note for consideration.
A "viking world" has a significant problem, in that the culture you're talking about (late-Norse) had as one of its centerpieces the act of going on expeditions. The name, "Viking", comes from the word víking, or expedition.
If your vikings don't have other people to go out and raid, they aren't vikings. And entire world of people who go out and making pirate raids on each other doesn't seem particularly sustainable. Your Vikings need, in some sense, the equivalent of a relatively wealthy mainland Europe to plunder.
Now, you can step back a bit to have your Vikings be somewhat earlier Norse, but those folks were a bit less battle-oriented.
That was what immediately leapt to my mind. A planet with a single unified culture is pretty weird, and gets into Futurama "Cowboy world" territory quickly.
http://tvtropes.org/pmwiki/pmwiki.php/Main/PlanetOfHats
Why not just run it in a fantasy earth? You have your mythology and culture already laid out. The maps are already done. Watch an episode of Vikings and you got a horde of NPC's.
I'd also agree with Tony Vargas that 4E really is the best D&D to run this type of game in, with the epic feats capable by martial heroes and playing to narrative tropes. 5E has a massive amount of baked in magic, and gutting it out might be more effort than its worth.