Thanks David for further explanation.
In the first round, the grading strategy Number of errors seems to be a wise and good choice to me. It makes the peer-assessment easier to cope with (for reviewers and reviewees, too) as it can focus on more formal aspects of the work. In the second round, more detailed peer-assessment can be provided via Rubric or Accumulative grading strategy.
With regards to number of instances (single Workshop versus two Workshops), it will be best to actually experiment and try both. I can see pros and cons of either way. It may depend on how you plan to do the peer-reviews allocations.
If the submitted work should be reviewed by the same peers in both rounds, then it is definitely much easier to have single Workshop. Just change the grading strategy after switching back to the Submission phase, leaving the existing allocations in place.
If you want to keep a record of how the submitted work looked like after the first round, it may be easier to have two Workshops.
Good luck, and please do not forget to share your teaching experience with the Workshop. It may take a while to learn all its features and bugs (sometimes hardly distinct ).