It is difficult enough for a committee of eight or ten people to plan an event like this effectively, but for it to be planned totally on-thread by everybody is just not feasible. It needs someone to co-ordinate it, preferably someone who lives in or near where it is to take place. Any offers?
The process involves:-
1) Most important - Making a list of everyone who expresses an interest (even a flicker of interest) and contacting them by PM, then keeping them updated at intervals. People don't always come back to a thread to see progress, and can forget completely about the event, if you don't keep them posted you then discover that they are doing something else on that day.
2) Finding out the most convenient date for everyone and settling on it.
3) Finding out what format appeals - start and finish times, what food and drink, will it be all socialising or a mixture of chat and "entertainment", any other ideas.
4) Getting approximate numbers. This will inevitably change, but you need some idea so as to book a suitable size of venue and get an estimate of cost from two or three places for space, numbers, menus. Keeping a note opposite each name when they confirm that they will be there, pay towards it, tell you their train gets in later, etc. - you think you will remember, but don't count on it!
5) Contacting possible venues and if possible visiting them in person. Deciding on a venue. Provisional booking.
6) Reporting back and checking with everyone that they will still be able to come so it is still on! Opening a separate account to deal with the money if that seems useful. Confirming booking and paying any deposit, and deciding whether to get a proportion of the cost back at this point or wait until nearer the time (having paid a little towards it does seem to make it more definite in peoples' diaries, so they are not likely to change their minds at the last minute)
6) Organising any activity or speaker(s). Keeping in touch with the venue.
7) Collecting money a couple of weeks in advance, so that you are ready to pay up when you get the bill or the invoice. Leaving it until the day only works for small numbers - if you try to receive and count cash and cheques while simultaneously chatting to everyone and solving last-minute problems you will be a nervous wreck.
8) Relax and enjoy it!