I love it even more than Terraria - if you go look at my steam profile I have spent more time in starbound than terraria and that was when it was still in alpha/beta. I love the game, the difficulty is a bit higher than terraria and it is awesome to travel the worlds.
We have had 5 or six - as long as you have a server then you can have as many people play together. I would collect materials - I tend to go get lost and dig a crater into worlds :P Then give the mats to the people who can design and build. The last server we had, we had a hovercraft as a base since that was safe. But then we got a server update and the base was destroyed due to meteorsSo we had to rethink it.
How many people can play together in Terraria?
I never got the hang of Terraria, I think its just the 2D style that doesnt grasp me, have played a lot of modded Minecraft, but just couldnt get into Terraria.