A fascinating story, with so many clever details from canon. The missing wand, and the fact that Peter is always shown as a weakling, yet he must have been excellent in magic to manage everything he did manage.
But morally, you've nailed him. A coward and a pathetic little rat. The contrast between his childishness and Ollivander's maturity is striking, and Ollivander's canon admiration is used very effectively here.
This is exactly the sort of relationship they might have.