This is important. A lot of people get all confused when they start taking more damage as soon as they pull out their healing spells. Well, no [censored], you just put your shield away. Obviously you're going to take more damage. Keep that shield out, always.
Shields really shouldn't add to armor though, that's not an illogical response since when you're not actually blocking with a shield it really
shouldn't be doing anything extra for you.
Anyway, my suggestion would be don't play a warrior for DiD unless you like chugging cheesy instant healing potions, pretty much awful gameplay.
If you still want to, sword and board is definitely better than 2 handers, dual wield is also better than 2 handers. Heavy armor is probably a better choice for staying alive through the early levels, even though light ends up superior at high levels due to the armor cap.