There is a USB hub chip inside to combine the two ports to one CPU port. So they're basically equivalent. Also like any USB, you can use an additional hub to have more than two ports.
There can only be one "root" drive, but you could plug drives into both ports, make one the root and the other a data drive mounted on a subdirectory of root.
I'm using a 32GB USB flash drive. I think that should be enough to run everything and store the necessary data.
The other USB port I'm going to use is as console port.
Thanks for the idea
For security reasons, I'd suggest to re-evaluate your plans - for OpenWrt 16 MB flash are already plenty, if you're thinking about 32 GB you're almost definitively doing something wrong.