Divine Family Tree

Water + Life = Plants
Earth + Life = Animals
Fire + Life = Monsters (beasts like ankheg and owlbear)
Air + Life = Dreams

Water+Death=Aberrations, Fire+Death=Demons, Earth+Death=Undead, Air+Death=Devils?

Re Races - You can limit the npc races, eg if you use 7 Players handbook races, then pick 7 humanoid enemy races and that's it. This will create a strong theme rather than the usual 'infinite variety of monsters' in standard D&D.

Also you don't have to quantify what every creature/portion of the planet is doing, just decide what ones are going to be involved in the story area you are using, and flesh them out.

Re Races - For the campaign you don't have to list where every intelligent humanoid race is located and what they are doing, you can just pick 5, eg-mind flayers, lizardfolk, hobgoblins, orks and duergar - then list what they are doing.

those not listed you don't worry about (eg drow, deep gnomes, goblins, troglodytes, cyclopse)-they are not major players in your campaign

this will give you recurring foes with goals, locations, and soon regional enemies and allies will develop to flesh out your campaign area.

in your case you can tie in your specific gods, so the nightmare god created mind flayers, envy god created duergar and so on.

Here is another approach you might try.
When I have 4 elements / 4 states I always want to put them into cardinal directions:

Water---------------Earth     Peace--------------Sadness
|                             |             |                         |
|                             |             |                         |
|                             |             |                         |
|                             |             |                         |
|                             |             |                         |
Wind------------------Fire       Joy---------------Anger

This is handy for visualizing the points at opposition: Fire-Water, Peace-Anger
However, in your cosmology mind and matter are intersecting or at least inter-related
If you place the two planes orthogonally, you get the following figure:

   Peace-------------------Earth
    /  |                             /  |
   /   |                            /   |
  /    |                           /    |
Water--------------Sadness |
  |     |                         |     |
  |     |                         |     |
  |   Joy-----------------|--Fire
  |   /                           |   /
  |  /                            |  /
  | /                             | /
Wind------------------- Anger

Now you have a d6 arrangement that creates some interesting relations
Air + Fire = Sun, but on the mind plane also Joy & Anger
Water + Earth = Moon, but so do Peace & Sadness

The faces of the d6 could be major deities, as in the sun & moon examples. Handy to note, sun & moon are opposed planes.
If I had to make up something for the other 4 planes, it would be:
Water + Wind + Sadness + Anger = Storm
Fire + Earth + Peace + Joy = Land
Water + Wind + Peace + Joy = Sky
Fire + Earth + Sadness + Anger = Mantle/Core/Lava

You can then pick any line between two points (edges) to create the full but reasoned list of combinations to draw from:
Peace - Earth = Plants/Growth
Peace - Water = Travel/Knowledge
Peace - Joy = Celebration
Water - Sadness = Loss/Tears
Water - Wind = Mists/Secrets
Earth - Sadness = Grave/Undead
Earth - Fire = Disaster/Turmoil
Sadness - Anger = Fear
Joy - Fire = Energy/Vitality
Joy - Wind = Song/Flight
Fire - Anger = Instinct/Rage
Anger - Wind = Lies/Spite

If you want to get into tertiary dieties, a good approach might be to use corners of 3 lines (vertices):
Plant/Growth + Travel/Knowledge + Celebration = Harvest & Education
Song/Flight + Energy/Vitality + Celebration = Symphony
Travel/Knowledge + Mist/Secrets + Loss/Tears = Lore
Song/Flight + Lies/Spite + Mist/Secrets = Mystery/Dreams/Omens
Plants/Growth + Grave/Undead + Disaster/Turmoil = Rotting & Rebirth
Disaster/Turmoil + Energy/Vitality + Instinct/Rage = War
Loss/Tears + Grave/Undead + Fear = Nightmare
Fear + Instinct/Rage + Lies/Spite = Treason/Betrayal

This approach lets you identify subordinates to the major dieties. For example, the top face, Moon (peace + earth + water + sadness) has underlings of: Harvest, Recycling/Rebirth, Lore & Nightmare. Logical!
This might lead to some odd situations in your pantheon, such as subordinate deities reporting to 2 or more major deities, or a situation where the tertiary deities have 3 parents... YRMV.

Switch any of the points around & assign your own major (faces) secondary (edges) & tertiary (corner) concepts or notions. It's an organizing principle and can be arranged in several different combos than the one I showed here.
Hope this helps!