I heard 'dude' used to address a woman. I also read in a dictionary that 'guys' could be used to address a mixed or even completely female group of people (but the same doesn't go for 'guy'). What would you say about that? Are these all limitations concerning the words' applicability to females?
Whether "guys" can be used to address a group of mixed males and females is debatable. I have heard people say that. It's not unheard of. I would not, as a woman might be insulted by it. Either because she thinks you are leaving her out by "only addressing the guys", or that you are insulting her femininity by calling her by a masculine word. It's easy enough to use other words that clearly can refer to both, like "folks" or "people" or something that specifically describes the group, "co-workers" or "friends" or "taxidermists" or whatever.
"Dude" is a word pretty much limited to very informal use in some sub-cultures. If you were having a business meeting of the company's accountants and you began, "Hey dudes ...", that would be considered distinctly odd. It's appropriate if you're talking to a group of surfers on a beach in California, or a group of skateboarders.