Mr Bennet says One cannot know what a man really is by the end of a fortnight. (chpt 2).

And later on Elizabeth says of Jane and Bingley:
She has known him only a fortnight. ... This is not quite enough to make her understand his character." (chpt 6).

I'm not sure if this means anything, but your post reminded me of the similarity in opinion on this matter between Elizabeth and her father.

As for your questions - I think Elizabeth is a studier of character. For example from the discussion with Jane in chapter 4 it is clear that she's not only observed Bingley and Darcy, but also Louisa and Caroline, and has formed ideas about their characters ("Their manners are not equal to his"). This sounds like someone who is interested in character in general, not just interested in handsome single young men. This is a different question as to whether Elizabeth is right in her opinions. Plenty of scientists have formulated plenty of wrong hypotheses without stopping being scientists.
For your second question, I assume by "valid" you mean "right". And I think we will have to make up our own minds about the rightness of Elizabeth's judgment about each character - certainly plenty of people have managed to form wrong opinions about someone else's character without pride being a factor.