You should not have been issued the eCOPR while outside of Canada, but it's unclear whether anyone would make an issue of this.I got the ecopr while in New York .
No, you don't need the PR card. You will need to apply for a social insurance number (given on the spot for new PRs at Service Canada locations) - that's what you need to work.
(You technically may be able to work without it if you've applied for a SIN and not received it but let's not go there.)