You cannot use the wand more than once per turn with these two features

Using a wand is a special action defined by the wand's description. The prototype wand says:

As an action, you can cause the magic wand to produce the cantrip [...]

You cannot produce a cantrip from a wand with the Attack action.

When you take the Attack action, Arcane Armament allows you to attack two times in that one action. Attack meaning to attempt to hit something with a weapon. But you cannot replace an attack with another action. And using the wand to produce a cantrip is not considered, in and of itself, to be an attack. Cantrips may have attacks as part of their effects, but producing a cantrip is not itself an attack.

When you produce a cantrip from the wand you have to use your full action to do so, which means normally giving up the option to Attack.

So, you cannot take an attack given to you by the Attack action and use it to use the wand to produce a cantrip.

To infuse an item, you need the nonmagical version of that item.

The artificer's Infuse Item feature states (TCoE p. 12, E:RftLW p. 57, WGtE p. 179; emphasis mine):

At 2nd level, you gain the ability to imbue mundane items with certain magical infusions. [...] Whenever you finish a long rest, you can touch a non-magical object and imbue it with one of your artificer infusions, turning it into a magic item. An infusion works on only certain kinds of objects, as specified in the infusion’s description.

The Artificer Infusions section at the end of the class description states (TCoE p. 20, E:RftLW p. 61, WGtE p. 181; emphasis mine):

The description of each of the following infusions details the type of item that can receive it, along with whether the resulting magic item requires attunement.

And finally, the description of the Replicate Magic Item infusion states (TCoE p. 22, E:RftLW p. 63, WGtE p. 182; emphasis mine):

[...] Alternatively, you can choose the magic item from among the common magic items in the game, not including potions or scrolls.

In the tables, an item’s entry tells you whether the item requires attunement. See the item’s description in the Dungeon Master’s Guide for more information about it, including the type of object required for its making.

Each of these portions I've bolded make it clear that you need a nonmagical version of the item to infuse, whether you're using Replicate Magic Item or one of the other artificer infusions.

Even though the Dungeon Master's Guide doesn't actually say "[X] is the type of item needed to make [Y]" for any listed magic item (as far as I know), this sentence seems to refer to the fact that each magic item that can be replicated is essentially an enhanced version of a clearly identifiable mundane item.

For instance, boots of elvenkind are boots, so the clear implication is that you would need mundane boots to infuse if you want to use Replicable Magic Item to make boots of elvenkind. This follows the same logic as the Boots of the Winding Path infusion (TCoE p. 21, E:RftLW p. 62, WGtE p. 181), which does explicitly state:

Item: A pair of boots [...]

In the case of your example, the description of cast-off armor states (XGtE, p. 136; emphasis mine):

Armor (light, medium, or heavy), common

Thus, you need a nonmagical version of whatever kind of armor you want to turn into cast-off armor. If you want cast-off half plate armor, you need a nonmagical set of half plate armor to imbue with that infusion.

The Replicate Magic Item infusion doesn't create a magic item from thin air - it gives you the ability to imbue a certain mundane version of that item with the necessary magic to function as that magic item.