This is a fascinating topic! Experience has led to garnering knowledge that can be applied to myriad aspects of this "thought-experiment." Plus, this is the sort of thing that many of my oldest friends enjoy "brain-storming" for fun & giggles, and I've shared scores of late evenings sitting round the fireplace discussing many things which interconnect with this subject.
First off, consult Joseph Cummins' book "CANNIBALS;" copyright 2001, The Lyons Press, ISBN 1-58574-217-1. He quotes at length from William B. Seabrook's book "JUNGLE WAYS" (1929) in which Seabrook avers that the human flesh which he had actually sampled, while in Africa, had all of the taste, texture, colour, and consistency of "well-raised veal."
Seabrook's contention was echoed in a psychologist's notes from lengthy interviews with an incarcerated human cannibal--- man-meat is really supposed to be almost impossible to tell from older veal.
Sorry; but that rather "shoots in the head" the idea that aliens might find human flesh uniquely toothsome--- with the emphasis on "UNIQUE."
If you either ignore this fact, or postulate that the aliens have more-advanced palates, or something, you might still be able to carry this off. Perhaps it's such that they raise cattle off-planet for their lower classes and Bureaucrats, but reserve "the authentic article" for the ruling class or Administrators. I do look forward to seeing this book.
Now, as for a line of thought which our "Ghoulish Gathering" has often explored, let me commend to you our delightful theory that ALIENS ARE ALREADY HARVESTING HUMANS FROM EARTH! Three of our number are Federal agents, and as a result, know a good bit about the statistics on the number of people who disappear or go missing, year after year. Another member, who occasionally joins our discussions by email, is with the European Union, and has access to data from overseas.
Evidently, up to MILLIONS of people "disappear," world-wide, every year. Now, most of these disappearances are in trouble-spots, where life is cheap and brief, or impoverished nations, where starvation or cannibalism is common. Still; something like 20,000+ people are alleged to technically "go missing" in the North Americas, the EU, and Russia, annually. Conventional wisdom contends that these are suicides, homicides, deliberate name-changing disappearances, and people simply "dropping out."
For the sake of fun, though, we've often supposed the "vanishings" are as you'd proposed: "Alimentary Abduction" of Humans by Aliens!
(Of course, we don't REALLY BELIEVE that; it's just fun to make spooky speculations!)
It's a perfect proposal: The aliens don't have to "spend" anything on maintaining their "farm." No expense or output to run it, at all, unless you care to suppose they have recruited (and put tracers on) human ghouls who're told of to hunt up specific sorts of people, on order. The ghouls would be tasked to find the specific "meat" desired, and take these people to pickup points, where they are then abducted by the aliens.
One winning scenario was postulating a luxury tour company that would offer "unbeatable deals" to "target groups" like the "alone" and single people; maybe even with fake contest prizes featuring all-expense-paid tours. The people leave on the tour, which turns out going much further than anyone expected!
It's a perfect plan for a truly frightening story! People on Earth have no idea what's going on! Governments aren't even aware it's a "problem!"
The alien species has no "overhead" aside from coming here, picking up a consignment, and going home---plus they get to eat very well, while away from Home-World!
If they must "pay" their human ghouls, their technology is such that they could either replicate currency or gold coins; or interdict a drug-cartel money-delivery. "Illegal money" is easy to find, with higher technology.
The aliens can keep their species' "luxury-niche" well-fed with only 20,000-30,000 "Alimentary Abductions" a year, for merely the expenditure of time and travel costs. And Earth Never Suspects!
Imagine the sort of meat-market if they've expanded operations and harvests to a million or more, each year? They have all these wars, plus the tribal and other genocidal pogroms, religious spats, and other diversions to cover up snatching one of two million humans a year to feed the Elite!