It's not even closed off is it- essentially a street?
Yes, it is a wide and long avenue. I think that most incoming streets will be closed and there will only be a few entry/exit points.
Nothing so far on where the stage will actually be, I mean which end of the avenue. On the poster, it is featured near the Place de la Nation end, but will it be its actual site ?
I'll go in the neighbourhood tomorrow to try to find out about it and will let you know. It can be relevant in terms of which métro or RER stations will be best to arrive and leave.