I dont know if this is the sort of answer you seek, as I have not had my OWN family yet but I have six brothers and sisters and numerous foster brothers and sisters. I find that sometimes you cant tell one sibling something and you feel more comfortable telling another its great to be able to have someone to confide in all the time[parents included]. Theres also days out, there'll always be someone to go on that rollercoaster or go for a coffee with, always someone to watch a TV show with or voice an opinion to. Worries are mostly sorted with a good ear to tell, unless its a personal depth that only you yourself can help yourself with. Theres so much to a big family.
Cons.... the fighting, bathroom space, fitting in one car, the oldest getting the front seat, trying to all fit round the dinner table, all the birthdays!!!! But it wouldnt be swapped for the world. Hopefully in a few years i can help with future aspects [money worries, etc]