I am wondering if I should get a boy or girl ragdoll cat and what are differences. And also good pair combinations like do two females go together, or two males, or a male and a female.
Male/female pairs do best. If they're spayed/neutered on time, of course! Male/male pairs usually are fine, too. Female/female pairs tend to get up to some rivalry eventually. It may not be bad but they rarely remain best friends for life, IME.
In general, males tend to be more laid-back, females tend to be more playful. There are exceptions, of course, individual personality is the important thing. A good breeder should be able to set you up with a kitten to match what you want in terms of personality.