im gonna go out on a limb and assume that i may not be the only person out there who isnt 100% sure how the ethereal plane is supposed to work.
The Ethereal Plane
The Ethereal Plane is coexistent with the Material Plane and often other planes as well. The Material Plane itself is visible from the Ethereal Plane, but it appears muted and indistinct, its colors blurring into each other and its edges turning fuzzy.
While it is possible to see into the Material Plane from the Ethereal Plane, the Ethereal Plane is usually invisible to those on the Material Plane. Normally, creatures on the Ethereal Plane cannot attack creatures on the Material Plane, and vice versa. A traveler on the Ethereal Plane is invisible, incorporeal, and utterly silent to someone on the Material Plane.
The Ethereal Plane is mostly empty of structures and impediments. However, the plane has its own inhabitants. Some of these are other ethereal travelers, but the ghosts found here pose a particular peril to those who walk the fog.
It has the following traits.
Alterable morphic. The plane contains little to alter, however.
Normal magic. Spells function normally on the Ethereal Plane, though they do not cross into the Material Plane.
The only exceptions are spells and spell-like abilities that have the force descriptor and abjuration spells that affect ethereal beings. Spellcasters on the Material Plane must have some way to detect foes on the Ethereal Plane before targeting them with force-based spells, of course. While it’s possible to hit ethereal enemies with a force spell cast on the Material Plane, the reverse isn’t possible. No magical attacks cross from the Ethereal Plane to the Material Plane, including force attacks.
starting w/ no gravity, i doubt they meant it to be an absence of gravity, such as 'you were standing on the ground, then the ground kept spinning, any you were not held to it by gravity so you are now a couple hundred miles away from the spot you went ethereal on, you may be inside the planet or out in space, consult a chart/roll a dice'.
so, we assume you maintain your inertias, linear and orbital, and cosmic.. (ie, earth spins on axis, wobbles in place, orbits the sun, and galaxy core, and possibly more..) except that movement on the ethereal is at half speed, so thats a monkey wrench..
if you go ethereal and 'drop' you weapon, it hangs in place at the spot you let go of it? if you use a projectile weapon it travels until it hits something (ethereal structure, force effect, creature,?). so your range is infinitish but, the projectile is limited to half speed? i know we have some maths floating around hear about CO arrows breaking the speed of light, but generally dnd arrows dont have a speed, so that half of zero may still be zero... or that is, projectiles maybe 'immune' to half speed bit.
no gravity, no 'ground' either, right? you can move up/down/sideways all you want, slowly... so while ethereal your effectively flying? your feet are not pushing on the ground, if you go under water your not swimming... if you go into a mountain your not burrowing.. that pretty much means your flying? now if you happen to have a regular flight speed thats base is worse than 1/2 walking but via feats and items is increased. say something like "+10ft" to your flight speed, your ethereal speed should be 1/2 base + 10 or something like that depending on your particular situation.
ok, gravity is abit of a headache..
lets see about "The Ethereal Plane is coexistent with the Material Plane and often other planes as well
" im digging out my copy of the manual atm, hoping for a diagram, but its not completely necessary...
these other planes, can you see them from the ether like you can the material? since the material plane is 4 dimensional, i assume that it takes traveling in a 5th dimension to get from line of sight w/ prime to line of sight w/ x.
if you can see some of these other planes, and do not have to travel to go see them, then you can see them at the same time as you see the prime? thats gonna get confusing.
how about air, you can breath on the ethereal right? is that the same air as the material? if i blow a balloon on the ethereal and take it to the prime and deflate it, does pun pun show up and smite me for polluting.
assuming the air is normal, you can make a fire on the ethereal, assuming you brought fuel. say that fuel is lamp oil, you pour some out, into a floating sphere (pouring should be a trick because you should need gravity to help) (while still on the prime you filed a water skin w/ lamp oil, cause you knew what you were doing ahead of time...) ok,, so you squeeze out a sphere of oil into the ethereal and ignite it, th outside edge catches fire and glows like a star? cool. that would be cool to throw an infinite distance... you could mock up a model of the solar system, except without actual orbits, that would require gravity and the model would fall on the floor.
thats it for the basics...
how about creatures that are native to the ethereal. take a ghost for example. they can manifest them selves on to the material anyway, but how about if they cast blink, or ethereal jaunt, or travels through a portal to the material, or the astral or the some non coexistant plane.
or blink dogs, if you take a blink dog to a non coexistant plane, can they still blink? are they still a dog? no wait, they probably are still a dog, but very smart dog.
ok, im gonna go finish looking for my manual of the planes, talk amongst your selves.