"여러분 and 여러분들" There is really no difference between the two as far as I know. 여러분 is already plural as you mention, but 여러분들 is also heard sometimes, especially when a specific group is mentioned. You might say it is redundant, but it doesn't sound particularly strange either. It can be considered a way to add an emphasis. Such usage depends on personal preference and habit more than anything else, as there is no rule about it. Generally, the plural suffix 들 is only needed when not using it will make the meaning unclear. Korean has no requirement on agreeing "number" between different parts as English does.

I know, but the thing is 여러분 already means "you" in plural form, so 여러분들 confuses me a little bit

I don't want to submit as an answer because I am not sure, but I think 들 is plural marker for when you really want to be clear it is more than one. but what I've learned is that plurals are not as regularly used as in English.