I am not the style police by any means but isn't a roggenbier normally at least 50% rye? I think what you have will definitely be tasty though.
Yes, but this would be close enough...
You could keep the rye at 20% and add 10% chocolate rye, but depending on how dark you want it, this may make it too dark. I'd keep it in the 7-10SRM range.
Assuming you have a good filter system, rye can be a b**** sometimes. Having said that, you want to crush it as fine as you can.