You lose all your money in the opening sequence and have to start almost from scratch. I'd say start from scratch, except you have reputation and other gang members. The money builds up pretty quickly.
After about 20 hours in the game, I can say I barely scratched the surface of what this has to offer. If you think watching guys getting killed by wolves was good, wait till you find an ancient vampire fighting two ice trolls.
One of the things I really enjoy about this is doing the quests when you see fit in a completely open world environment.
It depends on your goals. Are you going to prestige, if so, then put the double xp on leveling. If you don't plan on prestiging, put it on your guns. But remember, if you put it on your guns and your character levels, you may unlock a new gun that you prefer.
Lots of customization involved, which is why it's a RPG. And yes, you can hotswap a bow with a melee weapon, or walk around with a one handed weapon and have a spell readied with your open hand. You could even hotswap a spell and a shield.
You can buy a house, and some cities require it before they title you as a Thane. You can even decorate the inside of it. I haven't seen the married thing arise, but I'm sure there will be a side quest that requires it.
Cheapest death was by a merchant caravan. A dragon attacked, the caravan was fighting it off as well, the dragon was near death and one of my blows hit a caravan guard, so right in the middle of the fight the guards start fighting me. I killed the dragon, only to be hit from behind by a merchant and dying. So the effort of killing the dragon was for nothing.
If there is a chance, its a very slight one. Thinking about the various MW games, Infinity Ward's multiplayer aspect was Spec Ops. So I would expect more of the same, mission based multiplayer. Even after the success of zombies in World at War, they choose to stick to Spec Ops.
Also, another thing that sets Infinity Ward apart from the other developers is that they pride themselves on a game that is uniquely "Infinity Ward". So despite the popularity of zombies, I wouldn't expect them to use another developers niche.