I have had a group of 5/6 before, but it is complicated, and you do have to be prepared to seperate if it is not good for all the buns involved. I had to seperated a few times due to health problems, bullying and the like. Sophie has always been a dominant bun, however at the minute she is at the bottom. Charlies death caused problems and he was often peace keeper.
As has been said before you need to know your buns, and what is right for them, you need to have the space to keep them as a group comfortably and the space to seperate them without reducing the rabbits lifestyle if the group doesn't get on. And remember, it might not be just a case of seperating into two groups, it could be three or four depending on the size of your group. I ended up with one group of 6 in two singles and two pairs for a while, due to illness in the two singles which required them to be inside during winter, and the dynamic changing, so spliting the remaining group.
Personally I wouldn't take on x bun cos I wanted another bun ( although I have done in the past), or a certain breed has come up in rescue, and in the even of a death I look at the group dynamic before considering another one.
On the positive side, its fantastic watching a group of buns graze, and interact with each other, seeing how the group dynamic works, changes and evolves. And snuggles
big group pile ons
and being charged at by the group cos they know you have treats. Wouldn't change all that for the world, and hoping to get back to that point soon