I think I treat my close male and female friends the same. I tend to say more personal things with my female friends because I find women easier to talk to. Conversation subjects seem to differ. I talk about relationships more often with women and less personal topics (work, career, hobbies, etc,) with men. It's been a long time since I developed a crush on a female friend. That one worked out well because the feeling was mutual.
Same in some ways, different in others. There are things I will generally discuss only with men, that women would either not understand, would be judgmental about or offended by.
There are also things I would be more likely to discuss with a woman than a man.
My sense of humor would be different with the guys than with a woman. Not always or to the same degree, but women are typically more easily offended. A guy cannot let his guard down entirely with a woman, like he can with a guy. There is a certain chemistry between men that is just not possible between a guy and a female friend.
Yes, it is very possible to develop a crush on a female friend.