As an aside while you are writing all this is it possible to be mindful that the public server / public house analogy is not necessarily a neutral one? Recovery alcoholics and people who belong to cultures that do not drink may feel alienated by talk or bartenders and pub crawls. I personally found it offputting before I joined. It's not a huge issue but one to bear in mind.

As others have said above, making it easier for someone to invite a friend seems the highest priority to me.