How much of a commitment is joining the EDS?

This very much depends on whether you wish to act, and if so what part you have. It is important to realise that you will be part of a team and so you should inform yourself at the start of the rehearsal period and before you commit to a part in the play just how much time you will need to invest. Of course there are lots of jobs which will only require a commitment in the couple of weeks before the show is performed or during the performance weeks.