I can't help you much with eating habits, but I may be able to help you with
sex determination, since I was recently in the same situation.  Our
six-month-old "female" ferret, Scamper, turned out to be a neutered male
when I took "her" for a vet checkup!  Since he was neutered, there was no
penis to see, but the vet had me feel the midline of his abdomen, down near
the base of the tail.  You can feel a vertical bony ridge (more like
cartiledge) on a male, about an inch long.  This is a penis bone, the vet
said, and is found only on ferrets and dogs (I think she said).  If you feel
this ridge, you've probably got a male!
 
Other ways to tell are, of course, size (males usually weigh in at 3 lbs.
or more, females at 1 1/2 lbs.  or so), and face shape--males have broader
faces, while females' faces are more pointed.  A ferret book with pictures
can help you differentiate.
 
It has been an object lesson in sexism to me to discover that my sweet,
affectionate "female" is actually a sweet, affectionate MALE.  Up till now I
would have considered that a total oxymoron, but Scamper keeps proving me
wrong every day.  I guess we have more sex role hangups than we think!
 
                           Barbara
[Posted in FML issue 1492]