Is an arrow (bolt, bullet) considered a weapon if used as intended?

As stated in the title: is an arrow, bolt, or other object that is generally used as ammunition, count as a weapon when determining bonus effects from other feats/abilities? For example:

Dreadful Strikes – 1d4 psychic damage – TCoE, pg. 58

When you hit a creature with a weapon, you can deal an extra 1d4 psychic damage to the target, which can take this extra damage only once per turn.

It seems clear that hitting a creature with a sword via melee, or even a thrown weapon, like a dart or dagger, would benefit from this feature. But since Arrows and Bolts are “considered” ammunition, they would not (unless used in some other improvised way).

Does Witch Bolt deal the added 1d12 damage on the turn that it’s cast?

Assuming that Witch bolt is cast at 1st level and hits the target would the target take 2d12 damage in that turn because its the beginning of the spell’s duration and

"on each of your turns for the duration, you can use your action to deal 1d12 lightning damage to the target automatically."

or does it take effect the turn after you cast it?

Can Witch Bolt be repeatedly activated through a Wizard Scribe’s Manifest Mind ability?

The Scribe subclass of the Wizard has the "Manifest Mind" feature, creating a manifested spectral mind that can be moved by the Wizard as a bonus action. Additionally, the Wizard can cast spells through the spectral mind :

Whenever you cast a wizard spell on your turn, you can cast it as if you were in the spectral mind’s space, instead of your own, using its senses.

This allows the Scribe to cast spell remotely through the spectral mind .

The spell Witch Bolt can be cast through spectral mind , but it is not clear to me if it’s damage can be repeated if the spectral mind is within 30 feet, but the Wizard himself is more than 30 feet away.

The problematic part of Witch Bolt is the following:

The spell also ends if the target is ever outside the spell’s range or if it has total cover from you.

Is the target is outside the range, if the spectral mind is within 30 feet of the target, but the Wizard isn’t?

Can you warm yourself up with Fire Bolt?

During my last encounter my 3lvl wizard fell into a trap with freezing water below. He managed to save himself using Levitate, but during my party’s post-game discussion there was a question of getting out of freezing water into an even more freezing air (now wet through) and how it should impact a PC.

A spellcaster using a Ready action can keep any spell with a casting time of 1 action on concentration until start of his next turn.

When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs.

If it’s a fire spell and you hold its energy, then it seems reasonable it would release some heat, doesn’t it?

Also, even though you can keep cast and readied spell only until start of your next turn, Fire Bolt is a cantrip so you could just repeat the whole process as long as needed to get oneself sufficiently warmed.

And no, my wizard sadly doesn’t know Prestidigitation.

Is it possible to combo the spells Create and Destroy Water, Shape Water, and Lightning Bolt in order to make LB more powerful?

Asking on behalf of the group’s Wizard. He wants to electrocute the BBEG and have the spell deal extra damage through clever use of game mechanics. As a DM, I am all for it, as long as the rules somehow support it.

Create Water. You create up to 10 gallons of clean water within range in an open container. Alternatively, the water falls as rain in a 30-foot cube within range,* (PHB pg. 229)

Is this something you could cast, and either cast Lightning Bolt (8d6dmg) on the target being rained on(on your next turn / action), or use Shape Water to form a cube around the BBEG, and then Lightning Bolt to the face?

I personally think something being wet is conductive, which I might say means that the target being rained on would have disadvantage on the saving throw. My player really wants to try and argue that being wet yields a Damage Vulnerability (2x dmg), therefore causing lightning bolt to deal (8d6)*2 lightning damage.

Is there a rule I haven’t found in the PHB about this already? I do really want the player to feel cool, especially since this upcoming week there is a BBEG confrontation and this might turn the tide for my group.