#2 Assigning positions beyond those mandated by law (that is to say, secretary)
Chair is the only position mandated by law. The requirement to have a secretary was abolished in the Companies Act 2006, although I would strongly suggest having one anyway. You'll also need a treasurer as soon as the incorporation is done, so you may want to assign one now. I'd hold off on any other positions for now, if I were you.
As for the Mem and Arts, all I have at the moment is a mental list of ideas (let me know if and when you want them). There haven't been any real decisions made so far - that's your job!