Almost Guide.
Answer for request in comments Solar System (Repaired)
You need many time, some Tools (Text Editor with syntax highlight for JSON, Notepad++ as example) and a lot of desire for that.
Let's try...

First: Create Folder for You New mod: in folder "My Documents" follow "My Games\Stationeers". Create folder "mods". Then
Create folder "MyNewMod" (name it as you want). Copy Example mod (from .zip) or some workshop mod to "MyNewMod" folder.
Example mod you can find in game folder "??\Steam\steamapps\common\Stationeers\rocketstation_Data\StreamingAssets\ExampleMod.zip".
Workshop mod - "??\Steam\steamapps\workshop\content\544550\3319660622" (this is path for "Ellipso", see below).
To make NEW planet you must open game data folder "??\Steam\steamapps\common\Stationeers\rocketstation_Data\StreamingAssets\Data" (or some mod, much easy) and find file with planets settings "worldsettings.xml".

Copy the entire <World ID="PlanetName">..</World> section into a new file (don't forget to copy the header, and because of that - easiest way to use mod as a base). If you use mod as base - just copy file ("worldsettings.xml").
Ofcourse, you should choose a planet similar to you new world. I recommend choosing by Temperature, and change planet name to planet with wanted distance to the "Star" (Sol). For that you need edit Section <PlayableBody Id="?PlanetNameWithWantedDistance?">. You can choose existing planet (Vanilla) or determine you in file "celestials.xml".
This data contains info about terrain generation, atmos, other planets, space and more.

To change atmosphere and temperature - edit section <GlobalAtmosphere>.
<Key Time="0"> - temperature at midday
<Key Time="90"> - temperature at sunrise and sunset
<Key Time="180"> - temperature at midnight
To enable Seasons you must to create a new settings file based on "celestials.xml" from game data folder (or mod).
Add definition for NEW planet (edit existing) and change parameter "Eccentricity" to ? (depend what diffrerence between summer and winter, 0 - no difference).
I don't know tool for that. Change and check? As example you can look at mod "Ellipso" (Eccentricity=0.3).

About Gasses and pressure.
In game you not have possibility to add random mix of gases.
You must to determine what gases and in what quantity (in moles).
Pressure is calculated based on moles and temperature. If i'm not mistaken: Total 3 moles of gas (summary) in 1 cube (room 1x1x1, 8000 litres) with 20 degree of Celcius make pressure with 1 kPa. To calculate pressure with other conditions you can use formula pV=nRT, p - Pressure, V - volume, n - moles of gas (sum), T - temperature, R - constant = 8.31. Google for more info if need. If you don't want to count - just change amout of moles and see what happens in the game.

About Storms.
Never tried it so not sure if that is possible to add more than 1 type of storm (Bepinex possilble can do that). Especially depending on the season.

Additionally.
Remember, all Key words in settings - case sensitive, so better copy and edit existing files.
Naming of files: in mod it doesn't matter, only the extension matters (.xml).
Basically all settings can be in one file, but if you define new storm it should be in a separate file ("weather.xml" as example), or game show warning/error and storm not working. Almost same with "celestials.xml".
The "startconditions.xml" file determines How you start the game, respawn, and what you have at the start depending on the difficulty.
Want to change SpaceMap - look in "rocketlocations.xml".
Want create whole new star system (to observe with a telescope or eyes, if the planets is not too far away) - "celestials.xml". And you should edit section <CelestialBodies> in "worldsettings.xml".
--- END of INTRODUCTION ---

Continue ? ;)

For you world i would use Mars as base. Copy entire section <World Id="Mars">..</World> in new file as i wrote above. Remove property Priority, not needed. Rename Planet. Change Star name (if want). SolarConstant - how much radiation does a star emit.
Change PlayableBody to another if you need close or far distance from star, if you use moons, you need to copy <CelestialBodies> section from that Moon's world, otherwise the game will calculate distance to you planet (from the star) as from Moon to its parent Planet. Easiest way - use Planet.

Dont't forget you want a seasons. So you need to add "celestials.xml" (copy from "Ellipso", maybe need edit Eccentricity). Yes, i know that Ellipso has problem with launch (except me). You don't need to start, you need the source code.

In "worldsettings.xml" change section <GlobalAtmosphere> to:

I do not guarantee 250kPa at midday of Summer, this is close numbers that needed corrections. Also i have absolutely no idea how to calculate Summer/Winter temperatures. The settings above are for Summer.
But remember, during you winter with temperature -200 C CarbonDioxide cannot be spawned, because with that condition CO2 - is ice. And ice cannot spawned as atmosphere. Same with Pollutant. So in Winter you will only have Oxygen and Nitrogen. And because its sum only 10% of you standart atmo, pressure will also be much less than you want. And low temperature also decrease pressure. I guess something around 5-6 kPa.
As you can see, it is not easy to create good atmospheric mix, that "works" as intended. Also remember: CO2,N2,O2,"H2" in the atmosphere reduce the overall complexity of the world.

About Storm i wrote above. But you can try to add few "calls" in one world (planet). I'm lazy for that.
Example: find string <WeatherEvent Id="MarsDustStorm"/> (if you copy Vanilla mars. If not - add in section <World>, the next row right after <World> is ok place for this)
Add after:
Now you have all possible Vanilla weathers in one file. Work or not - leave comment (if you are still interested and try it).