Selljammer

That is definitely a cool way to do it, you definitely could have crystal spheres the size of a universe. I've just always loved the 3e cosmology since I read lords of madness and the manual of planes (not that it is any better than your method)

I've considered keeping the phlogiston in my games, but treating it kinda like hyper space. Its another conterminous plane, like the etheral, but you travel waaay faster in it. So ships can slip into the phlogiston, travel really far, then enter the material plane again once they reach a far away star.

Now what if they wana travel to another material plane entirely? Then they will need to travel through the deep shadow.

The alternate material planes I allow them to travel to will be really creepy. For example, in Dragon 373 an alternate material plane is described where Tharizdun had successfully destroyed everything. This plane is described as the home world of the Sharn.

There is also the home dimension of the Grell, which I have run on different physics, since Grell alchemy is some sort of wierd science that doesn't really follow the normal rules of the material plane.

Not a fan of 3e cosmology myself, though it's still leagues better than 4e. The plane of shadow is a much more boring Shadow World from Birthright. The Shadow World was a dark mirror, planar border, fairy world, and parallel world from which halflings originated. Travel to any other plane first passes through the Shadow World, sometimes things get stuck halfway. A place where illusion can be as real as anything else, that requires a special level of perception to see through.

I think the Elven Fleet deserves more use as an imperialist antagonist! Age of sail politics in fantasy space is the best way to run it in, though exploration and star trek style adventure is legit too.

>Called Spelljammer
>No one is jamming spells
This game is a house of lies.

I definitely feature the imperial elven navy in my games as a semi antagonist. They usually come across as xenophobic and heartless in my PC's encounters with them.

How do you come up with worlds effecitvley? I have a tough time when players just go to some random planet and I don't have much prepared for it.

their basically the east india company

The Brittish Empire in general, rather. Make a random table for cases like that, including the primary terrain that the majority of the population lives on, the dominant race, the general culture level, and maybe a simple quest hook.

Spelljammer looks fun and unique on the surface, but once you actually get to playing it, the themes are disappointingly shallow. There's actually nothing substantive about the "outer space" angle aside from weird gravity and limited clerical spells. You might as well just play a game where your PCs are pirates on the high seas. At least then it would be more grounded in one world. No one I've talked to who has played it has had a good time with it.
Elves are Chaotic Good, though.

You should have a general idea what's in each sphere before they even arrive. Most of a universe sized sphere is likely to be barren and lifeless, but there can easily be worlds where the Blood War rages, bases for the Scro empire or Elven fleet, a Tyrant Ship crash landed onto a weak world slowly but surely blasting it lifeless, or any number of things.

Consider having some unusual worlds too, like a Mobius strip or enormous drop of water on which islands float, while the depths hold metals in the form of some magical breed of coral.

their more neutral in Spelljammer

the Unhuman war was horrible on all sides and left its mark every where and on everyone

Not the Elven Fleet as a whole they aren't. The entire setting is clearly unfinished, and more a series of notes and ideas than a fleshed out setting. Things like air bubbles, the Phlogeston, casting in space and such all feel unfinished, but that shouldn't be too much of a problem. The high seas are never going to be as unusual as literally sailing through space. Being unfinished it requires more out of the gm, but there's enough to work with to have an appealing campaign!