For me, playing together with others is a way to give away work i do not like to do.
I'm usally mine enough ores for 3 bases in a few days and set up the gregtech machines.
But gathering food, Thaumcraft, Crops and building nice looking bases was mostly left to others.
And i did bees because no one else did.
If it's really just a single base, 4 players including me whould be the most, because with more there whould be not much left to do per player.
But, should we get 6 or more interested players, i whould suggest to make multible bases close to each other. x teams of 3 players building within a few hundred blocks. Sharing machines&resources. I would be fine to gather material for others, as long they turn them into a nice looking town.