For those that don't know, Artisan's blessing is forge cleric specific ability, as below:

You conduct an hour-long ritual that crafts a nonmagical item that must include some metal: a simple or martial weapon, a suit of armor, ten pieces of ammunition, a set of tools, or another metal object (see chapter 5, “Equipment,” in the Player’s Handbook for examples of these items). The creation is completed at the end of the hour, coalescing in an unoccupied space of your choice on a surface within 5 feet of you.

The thing you create can be something that is worth no more than 100 gp. As part of this ritual, you must lay out metal, which can include coins, with a value equal to the creation. The metal irretrievably coalesces and transforms into the creation at the ritual’s end, magically forming even nonmetal parts of the creation.

The ritual can create a duplicate of a nonmagical item that contains metal, such as a key, if you possess the original during the ritual.

There are a few points I want to know how they work:

1) If you want to break down a full plate, along multiple uses of the artisans blessing to make other stuff. What would you consider the value of the materials of a full-plate to be 'worth'? Is it half market-value, like what you need to spend on materials to make it, or its weight in iron, plus leather?

2) When using an item for this ritual, does the 'worth' of the item equal to its listed price, or its material components? If I lay out a shortsword, is it worth 10gp, as listed in the weapons section, or equal to its material value when using it fuel the ritual?

3) Can you make a box of chocolates? A metal box filled with chocolates "include(s) some metal"

4) As part of the ritual it says you need to lay out metal, can you use something that is 'some' metal, like a pike, or a barrel full of fish (barrels use metal bands)?

 5) It says it 'coalescing in an unoccupied space of your choice on a surface within 5 feet of you,' does this space need to be 5-ft maximum, or can you make a cart or wagon-sized object, so long as it is worth less than 100gp?

1)  It's entirely DM fiat letting you make plate piece by piece or not.  We don't have prices on the individual components.

2)  An item's value is its listed cost in the PHB or elsewhere.  The ability is in every way the equivalent of you paying your deity to make you an item, and your deity takes payment in barter.  The ability is fundamentally an item shop.  That's why the items you make *aren't* made of the same materials you sacrifice (you can and should use this ability to spend  copper on steel objects, for example).

3)  A box of chocolates is many objects, not one object, but the exact like between 1 object and Many is DM fiat again - it's possible to ask weirder and weirder questions, like "can I make a pile of iron shavings?", and ultimately your DM has to decide for your campaign what the limits are (when I DM, I always consider powders to be Many).  The ability also can make Many objects - one of the examples is 10 pieces of ammo, and another is entire toolkit.  Again, the exact limits are DM fiat.  Pray to your god and find out.

4)  A wooden stick with a metal bit at the end is generally ok, and so is a barrel.  Your god is not going to care about the fish, though, so using your ability on a barrel of fish is going to get you a pile of loose fish.

5)  The ability has no volume or weight limit.

1) Sorry, I meant if I have plate and I want to break it down, to use it as the material for the ritual. Plate is heavy and I want to make it into something lighter. Use splint mail instead for this example if you like.

Pretty much every one of these questions has the same answer "Ask your DM".

DMs could rule all over the map on your questions. Items could be valued at full market value or 1/2 market value. The market value in the world you are playing in might even be very different from the numbers in the PHB. In terms of breaking parts of an item down to make others and figuring out how much each part might be worth - ask your DM. Some DMs might rule the item parts only have value together and others might come up with some system of what each part is actually worth.

There is also the question of by-passing the 100gp limit in the blessing by breaking down what you are making into logical pieces that each cost less than 100gp. Most DMs would likely say no while others would allow it if it seemed to make sense to them. (i.e. making boots, greaves, vambraces, helmet, front chest piece, back chest piece - all separately)

The other aspect is that value is a combination of material cost + artisan time in creating it - does the blessing take into account the markup charged at shops? Market variations?

The bottom line is that the only person who can give you a definitve answer about how this would work in your game is your DM.

First of all, it doesn't talk about breaking things down at all. To me, that feels beyond the scope of the ability.

The term "metal" as the ingredients is very vague. I take this to mean raw material, which is why they had to specify that coins are okay too. The other argument for this is that, as you have noticed, when you broaden the definition to mean "anything with metal in it," there's a whole lot of other stuff you need to figure out which is not addressed at all in the ability.

If you decide that many things can count as metal, you'll need to figure the other stuff out with your DM. Personally I think this was meant to mean that a forge cleric goes around with a bunch of scrap/raw metal and uses it when needed to make stuff. But I guess it's kind of unavoidable that you'd find a bunch of armor or whatever in your adventures and you'd want to use it for your ability. If it were me I'd just go with half the value of everything, capped at 100gp. The way it is worded, even if you used plate as the "input" metal, the whole thing would transform into something worth 100gp or less.