I think, that you might be able to assemble morphs larger than you from the trace gasses there, of some sort, but the energy into matter theory is more probable. and, I would actually say that we have no idea how much energy the escaffi device actually gives you. it could all be left over from that... maybe.
I think, that they rescued the animorphs just by opening up the 3D space bubble to let them in. really, things can exist in zero space, including the andalite ship, for breif periods of time, at least. the 3D space bubble around the ship probably isn't necessary as long as you have air, I think, It's just an easier enviornment to work in.
(possible spoiler of book 13):
I think that zero space actually has distorted versions of the first four dimensions, necessary for anyone to exist in it at all. besides, if you look at the actual times required for the mass extrusion link to snap everyone back two there four dimensional anchor point, it was in order of their mass. because, tobias left first. so I think that there is some sort of potential energy in an imbalanced zero space mass extrusion system that causes this to happen only after it has become unbalanced in the fourth dimension also. stretch from earth to leera, no problem. stretch from earth in the morning to leera later that day, and BAM! well, actually, applegate used the word "pop" I think.