We'll start working our way through the LS4 story - off to Istan (though we start in Amoon). This is open to everyone - since this is a new story instance (and is the active story), anyone should just be able to make this story active. Only requirement is that you have PoF (sort of required to get to Amoon, isn't it).
Generally, each even runs about 1-1.5 hours, depending on length of chapters, etc. As many people as want to can sign up - we can split into smaller parties for the instances.