I have a slightly different take on this ... perhaps because I write stories for a living - stories that involve murder, torture and twisted psychology. So I think in story terms ...
For what it's worth, I don't think that any serial killer would go to all the trouble of paying for a series of operations and THEN killing the person he'd been transforming. Killers are gripped by compulsions. They want gratification. They're very unlikely to want to defer that gratification for months and months. So either the whole thing is just a lure to ensnare vulnerable MTF transsexuals without any intention of funding a single procedure (although God knows there must be simpler ways of doing that)... or he really does get off on the idea of transformation.
If this man were one of my characters, I would portray him as someone who buys other girls the operations he would love to have himself, but does not dare. So he creates perfect surrogates, turning them into the perfect women he, too dreams of being. In this scenario, his intentions would not be murderous ... but they would of course be manipulative and possessive.
If he creates the new you, then he owns the woman you become. You're bought and paid for. Now, many a girl knows what it's like to have a life funded by a man, and the perils of that situation are obvious. But I can also see the attractions of the situation, too, both from your point of view ... and his.
And it's not such an unusual story, after all. One of the most popular, beloved musicals of all time tells of a man who transforms a woman, falls in love with her, feels he possesses her, loses her ... but then wins her back because she chooses to go to him ...
... My Fair Lady
