First of all, I don't think you should worry about parades. I for one don't think it's a good idea for the parade to go down Main Street´, but I don't know what others feel about that? Of course if you do want, ya know, the big parade on Main Street, the middle could be a problem...
But if you have the middle there already, I can't see the trees being the issue? Oh and don't worry, there will be trees plenty of other places, this is just a small start...
But the road itself will be about 5-7 meters on either side (not including the sidewalks) and shouldn't that be enough?
I can see the problem in this not being Main Avenue, so perhaps you're right? But I'm gonna leave it as it is at the moment and see how it looks when there's more done, since it easily can be removed...