Possibly long thread, and all tips may not be universal - just reporting on my experience.
And a previous version had made it to review for a French grant the year before but was rejected. The feedback was very important to fix issues with the workplan and get my ERC application in shape.
HOWEVER... Part B2 gets you funded. I started by writing B2 and made it as mature and airtight as I could. Then decanted the essence into B1.
Some criticism was brutal but it helped me spot weaknesses in my application and fix them.
(Offer not applicable on this thread I'm afraid)
I had 10 minutes to pitch the project - the form had to be super polished.
However, I arrived at the interview feeling prepared.