Can a wizard prepare new spells while blinded?

For a wizard, preparing new spells at the end of a long rest seems to require studying their spellbook (emphasis added):

You can change your list of prepared spells when you finish a long rest. Preparing a new list of wizard spells requires time spent studying your spellbook and memorizing the incantations and gestures you must make to cast the spell: at least 1 minute per spell level for each spell on your list.

Assuming a wizard’s spellbook is a mundane book or other written medium, does this mean that they cannot prepare new spells if they are blinded at the end of a long rest? What if their spellbook is something more exotic, such as a spellshard?

What creatures cannot be blinded?

Warlock with Beshadowed Blast can blind targets if target fails to make a DC check against 10 + Spell level (4) + Caster level

Beshadowed Blast indicates:

This eldritch essence invocation allows you to change your eldritch blast into a beshadowed blast. Any living creature struck by a beshadowed blast must succeed on a Fortitude save or be blinded for 1 round.

And blinded creatures are:

The character cannot see. He takes a –2 penalty to Armor Class, loses his Dexterity bonus to AC (if any), moves at half speed, and takes a –4 penalty on Search checks and on most Strength- and Dexterity-based skill checks. All checks and activities that rely on vision (such as reading and Spot checks) automatically fail. All opponents are considered to have total concealment (50% miss chance) to the blinded character. Characters who remain blinded for a long time grow accustomed to these drawbacks and can overcome some of them.

What sort of creatures does not need to make this save since they can’t be blinded?

Can a Blinded caster with Blindsight use spells that require them to see the target?

The situation I have in mind is the following:

An epic battle ensues between a Young Green Dragon (caster variant) and a Purple Worm. The Purple Worm swallows the dragon; meanwhile, the dragon has blindsight and can cast Command.

Command is a spell that requires you to see the target. However, the dragon is Blinded (so it can’t see) while swallowed. It has blindsight out to 30 ft, though, so it can perceive its surroundings without relying on sight.

Can the Young Green Dragon use the Command spell to have the Purple Worm retch it out?

The general question is: does the interaction of the Blinded condition with blindsight still prevent the caster from using spells that require them to see the target?

There is another question which asks if creatures with blindsight can be affected by the Blinded condition. The answer is yes, and we begin this question with the fact in mind that the caster is both Blinded and has blindsight.

When blinded, could I use Detect Evil and Good to target an enemy?

I’m planning on running a Monk/Cleric (14 in Monk and 6 in Cleric, if my character survives that long, I haven’t yet multi-classed into Cleric), and we’ve come across a few enemies that are able to blind members of our group, and as a halfling, I don’t have the benefit of dark vision (which is fine, we have members of the party who are able to light up the room).

But with some of the context out of the way, Detect Evil and Good states:

For the duration, you know if there is an aberration, celestial, elemental, fey, fiend, or undead within 30 feet of you, as well as where the creature is located.

As I wouldn’t be concentrating on another spell, I should be able to make unarmed strikes while using this spell, but that leads to the question:

Would I still have disadvantage on my attack rolls (while blind) as a monk, if I know their location via this spell?

Can you target yourself while blinded or invisible?

Several spells, like Healing Word and Hold Person, require you to see your target. Does this mean that you aren’t allowed to target yourself with spells that require you to see your target when you’re blinded or invisible? For reference:

Healing Word

A creature of your choice that you can see within range regains hit points equal to 1d4 + your spellcasting ability modifier. This spell has no effect on undead or constructs.

Hold Person

Choose a humanoid that you can see within range. The target must succeed on a Wisdom saving throw or be paralyzed for the duration. At the end of each of its turns, the target can make another Wisdom saving throw. On a success, the spell ends on the target.

5e Inside Giant Toad, blinded and restrained but also unseen, disadvantage to attack the Toad or not?

When swallowed by a “Giant Toad” you are “Blinded” and “Restrained” giving you disadvantage on attacks.

However you also have “total cover against attacks and other effects outside the toad”.

The Toads eyes are outside the Toad, I certainly don’t see anything inside my own stomach, so doesn’t this mean you are considered Unseen when swallowed?

PHB: Chapter 9: Combat Unseen Attackers and Targets (pg 194-195) “When a creature can’t see you, you have advantage on Attack rolls against it.”

So the Disadvantage and Advantage Cancel out. And an attack against the Toad from within has no advantage or disadvantage.

Question is this then:

Am I unseen while swallowed?

Can a Divination use the Portent feature on themself while blinded?

The blinded condition states (emphasis mine):

A blinded creature can’t see and automatically fails any ability check that requires sight. […]

Meanwhile the Divination Wizard’s Portent feature states (emphasis mine):

[…] You can replace any attack roll, saving throw, or ability check made by you or a creature that you can see with one of these foretelling rolls. […]

It seems clear to me that a Divination Wizard could not use the Portent feature on another creature while the Wizard is blinded because the target would no longer be a creature they could see. However, I’m unsure how this applies when changing one of the Wizard’s own rolls.

Can a Divination Wizard really use the Portent feature while blinded but only on their own rolls?

If I’m blinded, can I cast a spell that doesn’t require that the target be “a creature you can see”?

I’m playing a Wild Magic Sorcerer who obtained a Wand of Wonders — randomness ftw! Anyway, I accidentally blinded myself by using the wand.

On my next turn, still being blind, I want to cast Acid Splash on a target — can I do this?

I attacked the target before, and they haven’t moved, I chose Acid Splash because the spell doesn’t need “a target you can see” (unlike Hold Person, for instance). I did have line of effect, not line of sight, but I don’t think I need it for this spell.

The DM wouldn’t let me cast it unless I rolled to see if I targeted the enemy or an ally standing next to it.

We couldn’t really find an answer to this, so I switched to Ray of Frost and rolled with disadvantage, as that is all Blindness does to your attacks.

Can someone point me to the right page in the PHB, or just tell me who is right? (I know the DM can always make his own rulings.)