DreamObjects will have no problem handling that many files! That's actually what it's designed for.
The interesting thing about object storage, in general, is that it doesn't care about folders. A bucket is a flat namespace and folders are just simulated for the benefit of visual organization. For example, let's say you have a hard drive with images in a folder structure like this:
(That's supposed to be a Vacations folder with Hawaii and Skiing subfolders, each with a couple pictures in them.)
When these are stored in DreamObjects, the files are stored with folders in the name, so it actually looks like this under the hood:
This makes accessing your images from DreamObjects pretty straight-forward, it's just /Vacations/Hawaii/beach.jpg
And the really nice part is that URL can be an alias so it can be your domain. You can even turn on CDN and really accelerate the delivery of those images.
I hope that helps explain a bit.