In terms of logistics and how a room is laid out, I think that probably, the reason most clubs will put a performer at the end of a room and not in the middle is primarily for reasons of access for the audience. Not just things like access in emergencies, although clearly, these considerations have to be uppermost in any organiser's mind, when he is, in effect, inviting the public to a venue he (generally) has no practical control over. Simple things like minimising disruption to a performance, by people wanting to go to the loo, or nip out between songs to the bar. It's a lot easier if they aren't having to shuffle past the stage

That's just a comment - I really don't feel qualified on contributing to what makes a good folk club - beyond what has been said already. Any club that has kept going for even five/ten years is a success