I had thought at the time that there was way too much energy to be channeled through a single dilithium crystal for the entire ship, or even the FOUR crystals we hear about in "Mudd's Women." That's why I kind of thought it probably went the other way (and bear with me on this idea) that the dilithium crystals actually catalyze the creation of antimatter which is then sent to the reactors in the nacelles for consumption. Some power is drawn off from the nacelles and sent back down to engineering where it is conditioned and rectified by a very large transformer assembly (behind Scotty's chainlink fence) and distributed throughout the ship. The reason I came to this conclusion is that various metals (gold, for instance) can be used to produce positrons when struck by high energy photons. I suppose that there's something about dilithium that when you set it as the target for a high-velocity particle beam (in a conventional TOS setup or a TNG-style warp core) the incoming particles deflect off the crystal with reversed spins/charges and are thus converted into antimatter. The resultant antiparticles are drawn off and sent to the nacelles where their mass is converted to energy. Meanwhile, the ramscoops in the warp nacelles gather hydrogen from the interstellar medium to be reacted with the antimatter, with excess hydrogen being pumped down to engineering and fed to the converter assembly to be flipped into antimatter (so their power "regenerates" over time, as long as the warp engines are operating; if not, they'll burn the hydrogen in the impulse engines). This way I kind of disagree with your #3, that the only source of usable power for the ship is the dilithium crystals; from "Elaan of Troyus" it's implied that the main source of power is the warp drives themselves. But from that same episode, there's something else a little worrisome: Scotty initially tells Kirk "the antimatter pods are rigged to blow up the moment we go into warp drive!" But later he tells Kirk "The entire dilithium converter assembly is fused, no chance of repair." Those appear to be separate, unrelated problems, and apparently the first problem cannot be resolved "without being blown halfway across the galaxy." But Scotty only corrects the latter problem with Elaan's necklace... so what about those sabotaged antimatter pods, and how come nobody mentions them again? The most likely scenario is that the antimatter pods--located in the nacelles--are fed FROM the dilithium chamber and contain the reserve fuel supply for the warp engines. This would explain why Scotty didn't realize the converter assembly was fused until later; he simply realized that the crystal was no longer producing antimatter and that activation of warp drive would cause the flow of "bad" fuel into the lines where it would explode on contact with the good fuel already present.