Videos:
Watched about 8 of them all the way thru.
Scrubbed thru a few others.

As much as preparation helps, your videos could benefit greatly from more post production work.
Per video there is 0-3 cuts that seem to only tie together multiple recordings.
With more editing your average of 10-20 min length could probly be cut down to 2-5 min and still contain the same general content.
Sliding in some images digitally to supplement what you are saying could also help.

I can recommend this book on film.
It's been years since I read it, and can't seem to find it on my shelf, but if its the book I'm thinking of its rather good.

Conversation:
I read the entire thread.
It's evolved quite a bit.
In its latest form I perceive that this is almost like some sort of experiment that Alex is running.
Seemingly random information is presented.
Viewers (mostly Helm) react.
Reaction is analysed and more random information and questions are presented.
Why? What then? How come? What about? So? Why? Why? Why?
From what I remember, this is what children do.
And I don't mean that offensively, to say this is "childish", I mean literally children.
They learn by throwing rocks and seeing what happens.
Shouting words and listening to what people say back.
Thru this data a definition can be created, in this case -> self.
That may not at all be the intention, but it's how I perceive the situation overall.
If that is on some level whats happening, that's fine.
It seems to be fueling more videos and perhaps another book.
Productivity is a good thing.
The only part that's not so great is Helm is giving very solid life advice, and its being pushed off as something like robotic bullshit.
If that's part of the whole ruse go ahead, but a nod or wink might put everyone more at ease.
Alex you may want to consider trying some sort of Tom Green Show/Jon Benjamin Has a Van/Borat type of thing where you run around and get reactions out of people.
Its a highly marketable genre and not many players in the field.

Humor:
As serious as this has been I found that if you sing snippets of Helm's posts to a rock guitar, and rap portions of Alex's text to a beat, its !@#$ hilarious.
Try it.

Thoughts:
This whole exchange is interesting, and I actually applaud those involved for having, and keeping, it in public.
In my observation of others, and own experience, I've found that the more vague and fuzzy we perceive things to be, the more "unhappy" we are, and less likely to be productive.

The grid-picture is especially interesting.

Here's how that works in GG:


I use this quite a bit.
Even on sprites and compositions not meant to fit tiles.

Create a grid size. <---- usually your tile size but could be anything.
What size sprite do you want to draw?
1x1, 2x1, 1x2, 2x2, 3x3 etc?
I like to write the size next to the character to remind myself.

Relative dimensions help the process of design and create a simple basis of scale across all sprites:



Personally I don't count small bits that go over the line, just the main masses. <--- usually based on where the sprite contacts the ground.
But fitting to the grid exactly can also be a good thing.
Depends on what you want.
Of course this works great for tiles too.

Also use Snap with the Select tool to move things around quickly.
Works great with other tools as well, such as Filled Rectangle:


Try it!

Mini crit: the fs doesn't quite convince

I notice a bit of, perhaps unintentional, visual repetition <-- "Twinning":


Basically the eye does relatively the same thing 3 times as it moves across this area of the image:
bump, bump, bump.
instead of:
Bump, buuump, Bummp.
Its really not that big of a deal, and is only as relevant as you want it to be.
But its a fun thing to use to your advantage. <-- create pattern, focus, relation, symmetry etc.
Or actively look out for and remove from parts of an image <-- most artists naturally twin on a first pass, so its sometimes easier to think about on a cleanup pass.
Cool painting!

Aquaman lives in the sea and doesn't look even remotely fishy.  Just sayin'.  

Its a very subtle amount of visual theme but his old costume has scales and fins:

Some of his other designs are less fishy.

form as derived from fuction

Yes!
Function and form go hand in hand.
What's it for?
What's it do?
How does it look?
Does how it looks affect what it does?
Does what it does affect how it looks?
These are important questions when coming up with stuff.

I added a fin, but it looks quite odd lol

Function and form are probly why you think the fin looks silly.
You've added a form but are unsure of the function.
Why did you put it there?
There are different levels of function.
Does it help him swim? <---- function of action
Does it make him more fish like? <----- function of theme
Does it balance the composition of his overall shape? <------ function of art
Does it just look cool? <------ funciton of appeal
Be self aware of why you are adding a prop or feature.
It will help give you direction for the specific feature you are working on.
You'll need to convince yourself to alleviate the feeling of silliness.

but I do apologize for not giving any detail/information as to where the race lives ect.

No need to apologize!
I just wanted to point out that expectation has an affect on perception.
Make the design your own and have fun with it.

Your words "a rather aquatic race" sets up an expectation in the viewer.
Most of this expectation is implied as no other information is provided.
The common thought that comes to mind is that this guy lives underwater.

Anatomy design has many factors.
An important one is mobility.
Creatures use their adapted bodies to move thru their environment.
Certain forms and features are better suited to specific environments with specific types of mobility.

Of course an adapted body is not necessary for specific types of mobility with the power of technology.
People cant fly so they use airplanes.
People cant run 70mph so they use cars.
From this characters body and features I imagine he would need and be able to develop similar technologies to get around underwater.

Visual theme carries a lot of power (and because art is visual this is important).
Its not necessary at all to design an aquatic character to have extreme fish like features.
However it makes him quickly readable, relates to the natural world, and distinguishes him from characters of other enviroments/classes.

Of course character design isnt nature or science.
Its enough to just make something cool, whether it fits how we relate it to the natural world or not.
Telling the viewer what something is has a lot of power.
Just keep in mind that without telling us anything, would we all come to an agreement of what this guy is, where he lives, etc?
An easier description to swallow might have been "a race that uses water magic".

Two great pieces of advice that have always stuck with me:
1. "Show me, don't tell me"
2. "Always error on the side of more extreme"
The idea being: try stuff, and if it turns out really silly, it's easy to remove.
Pushing a design on paper can reveal appealing options that seem ridiculous in the mind.

But I'd say dump all of my design choices here and come up with your own.
It's obvious that you are going for something different than a fish man.