What counts as a spellcasting focus for bards?

Inspired by this question: Can a multi-class spellcaster have one thing be two different focuses?

The PHB, on p54 says:

Spellcasting focus

You can use a musical instrument (found in chapter 5) as a spellcasting focus for your bard spells.

And yet on p53, the PHB in the introductory description of bards, gives examples of three bards:

Bard #1:

Humming as she traces her fingers over an ancient monument in a long-forgotten ruin, a half-elf in rugged leathers finds knowledge springing into her mind, conjured forth by the magic of her song—knowledge of the people who constructed the monument and the mythic saga it depicts.

Bard #2:

A stern human warrior bangs his sword rhythmically against his scale mail, setting the tempo for his war chant and exhorting his companions to bravery and heroism. The magic of his song fortifies and emboldens them.

Bard #3:

Laughing as she tunes her cittern, a gnome weaves her subtle magic over the assembled nobles, ensuring that her companions’ words will be well received.

In each example, the implication is that the bard is casting a spell, and the implication is that the action of the bard is central to the magic, and at least to my reading, that the voice, sword/mail, and instrument are spellcasting foci. Maybe it is meaningless fluff, or maybe the implication is that those are all spellcasting foci.

There are two parts to my question:

  • Is it reasonable to assume that RAW or at least RAI that the implication is that in the case of bards, they can use 1) their voice, 2) an improvised musical instrument, or 3) a bought musical instrument?

  • And if such an assumption isn’t RAW/RAI, what are the implications to allowing it as a house rule?

How does the Ring of Spell Storing interact with the Glamour Bard’s Mantle of Majesty feature?

At level 6 Glamour Bards gain the ability Mantle of Majesty which allows them to cast command up to 10 times (ability lasts a minute and command is cast as a bonus action) without expending a spell slot:

you take on an unearthly appearance for 1 minute or until your concentration ends (as if you were concentrating on a spell). During this time you can cast the command spell as a bonus action on each of your turns without expending a spell slot.

Does this mean that I could activate the ability (outside of battle) and then store 5 castings of command in a ring of spell storing for use at a later time?

Does the bard’s Inspire Courage feature increase damage for swarms?

The Bard’s Inspire Courage feature references weapon damage rolls:

A 1st level bard can use his performance to inspire courage in his allies (including himself), bolstering them against fear and improving their combat abilities. To be affected, an ally must be able to perceive the bard’s performance. An affected ally receives a +1 morale bonus on saving throws against charm and fear effects and a +1 competence bonus on attack and weapon damage rolls. […]

This clearly included Natural Weapons such as a Claw or Bite, but does it also apply to Swarms’ automatic damage?