1)“零零几的车牌”
I am not sure the context of this expression. But I can give you another example, if people say "O字头的车牌", it implicitly means that the car belong to local government, also it means these vehicles have high priorities than other cars. Might “零零几的车牌” has some specific meaning in certain context.
2) “越绕越糊涂”
it means someone want to explain something to you. But the more she or he explain to you, the more confused you are.
3)“聚众殴打”
I think it simply means fight in group. For example, after a party, two group fight each other for something.