Definitely get as many ADRs now as you can. If you can be flexible with your times, you should be able to get what you want.
But you should DEFINITELY do your ADR's now. We just got back 2 days ago and I overheard several people being turned away who didn't have ADRs and just wanted to walk in.
You can possibly get into a place after you have arrived. We managed to get an ADR for LeCellier the day before we went.....we didn't go til 2:50 which is at the end of the lunch service. So if you can be flexible you should be able to go where you want!
I didn't book most of our ADR's til about 2 months out and I got everything I wanted. Maybe I just lucked out!