...and beagan duine translates exactly the same but is a phrase more appropriate for a cannibal asking for seconds.
Would beag be bheag if this was about a female person?
The word for woman, boireannach, is actually masculine.
Would this be an acceptable interpretation if you were talking about one of the "little people" (a fairy, for those who aren't familiar with Highlands and Islands mythology)?
Am I correct that duine beag also means a little man?
Yes, man or person.