Plate Armor reducing you to one movement die doesn't seem affected by the carrying of Chests in Prince Magnus' Gold. It also doesn't account for other later modifications to the player's movement dice (if you were rolling five movement dice, would you be reduced to 1, would it be cut in half or just reduced BY one with the Plate on?).
I think the most sensible way is to apply the movement penalty first, THEN add on any bonuses to movement from spells, artifacts, potions.
As for body Armor, in the EU editions it seems like the armor is meant to "re-calculate" your base defense while worn. This can be confusing, but it comes out the same.
So you have 2 base defense, but when you put on the Plate, suddenly your base is 4.
In the NA edition it clarifies that body armors simply add dice... for example Plate just adds 2. So Base defense 2 + 2 = 4. Shield and Helmet each add 1. Bracers add 1. Cloak adds 1. Chainmail adds 1 (or resets your base defense to 2 in the EU rules).
It doesn't mean Chainmail gives you 2 extra or Borin's Armor/Plate gives you 4 more. That would be insane and I don't think was the intention! It means you'd be rolling 8 dice just from equipment (remember that spells and potions can add even more defense... Rock Skin adds 1 in NA but 2 in EU... potion of defense adds 2, etc). But the number of dice in the box doesn't limit your rolls. If the situation calls for it, you roll as many dice as you are supposed to!
Many debates were once held over Borin's Armor, but at least in the Remake it was clarified that it is simply magical Plate Armor (+2 defense, no movement penalty) and can be combined with a helmet and/or shield.
Some things aren't made perfectly clear but are guessed from logic. So you can only wear one helmet, and only one set of body armor (but bracers and cloak could be combined... though in the Remake ---which doesn't have the cloak---rules it seems Bracers could be combined only with the helmet and/or shield not another body armor).
What about the Wizard's Cloak? I would imagine they intended for the Wizard's Cloak (for Wizard or Warlock only) to be able to be combined with Bracers as in EU edition having the cloak/bracers combination but it was probably an oversight that they didn't mention this.
Otherwise logically you could carry two shields (but therefore couldn't attack because your hands are full so you can't hold a weapon).
