I would chop it into at least bite size pieces for easy cutting/serving. Smaller sized pieces would be OK too but if I were eating broccoli rabe I might like to see and taste variation between the leaves and the florets. If the florets are big slice them in half lengthwise before chopping.

Yes, blanch it for two minutes in boiling water, starting the time as soon as you put the rage into the pot. Then plunge into ice water to stop cooking. Regarding chopping it, you can do it before or after blanching.