The spell astral projection creates a copy of you on the astral plane, and gives you the chance to create a copy of yourself on another plane if you travel to it. Is there any information out there on how this is accomplished? Do you swim to the other plane, and how fast do you travel? How does one 'navigate' to another plane? I've got homebrew ways of doing this, but I'm wondering if there is an official way (or even unofficial-but-generally-accepted-way) of handling this.
Anyone?
Nope. It starts generally falling under homebrew territory. Most planar adventures do.
Astral Plane.
From that I can tell you that you travel 150' 1st round then 300'/round thereafter until you try to stop.
The strength of gravity on a plane with this trait is the same as on the Material Plane, but each individual chooses the direction of gravity's pull. Such a plane has no gravity for unattended objects and nonsentient creatures.
Characters on a plane with subjective directional gravity can move normally along a solid surface by imagining "down" near their feet. If suspended in midair, a character "flies" by merely choosing a "down" direction and "falling" that way. Under such a procedure, an individual "falls" 150 feet in the first round and 300 feet in each succeeding round. Movement is straight-line only. In order to stop, one has to slow one's movement by changing the designated "down" direction (again, moving 150 feet in the new direction in the first round and 300 feet per round thereafter).
As to how long it takes to find a portal to a specific plane - As long as it needs too!
scroll down to movement and combat This is from AD&D planescape I think, but might help.