Extremely Smart Calendar app needed! Does anyone know of a calendar app that could handle a bunch of iCal events, each dependent on their timing for the placing of the final one, so that the final date could be copied and moved and all the others would stay the same distance apart?
For example I might have an irregularly recurring event which is a concert. Two days before that I need to hold a rehearsal and book a hall three weeks before the rehearsal. Five days before the rehearsal I need to have all the music notated and send it out to the performers. At least a fortnight before that, on the nearest Monday afternoon, I need my calendar app to invite my performers to take part and then report back to me whether or not they are available. I then have to start notating music to suit the line-up I can get. I need to allow 50 hours of free time to do this task, so it needs to slot in with spare time I have from other events I might be managing.

Having spent hours setting all that up once I wouldn't want to do it again. I would like an app that can take all that and call it one event which can be kept in a library and assigned with the final event to any date of my choosing. It would then work out everything else backwards and tell me when I need to do all the tasks on my calendar. 

Does anything like that exist?
Plenty of Calendar apps, such as Fantastical, can parse your needs with natural language, but I am not aware of any that can string together all your events as you have stated. 

However, you can certainly do this with Automator/AppleScript and iCal. There are many resources on the web that will give you instructions and snippets that you can string together with Automator without any programming knowledge. Many of those scripts can be found here on AskDifferent.