"By Any Other Name"
1) The Kelvins did not have to take the human form to adapt to the Galaxy, but use them to acclimate and observe. Their true form (if any) is utterly horrifying to the senses (The Full Lovecraft, boys and girls).
2) The barrier at the Edge of the Galaxy did rupture their vessel (who's set of physical laws didn't take kindly to it) and they had to crash within range of the ship. While primitive, the ship with modification will serve thier needs.
3) The return to Andromeda is something of a misnomer. The Kelvin Empire has a outpost in one of the Magellanic clouds and is preparing an all out invasion force for the Alpha and Beta Qudrants in thier "Ships?" (Technoorganic nightmares)
A brave little theory, and actually quite coherent for a system of five or seven dimensions -- if only we lived in one.
Academician Prokhor Zakharov, "Now We Are Alone"