They don't have to get the Euro (and might not qualify) but would have to meet and follow strict controls
No, as a new member of the EU, Scotland would be required to take the Euro. This is one of the core requirements for new EU members and they have no choice in the matter. The same goes for Schengen.....
Now, the only way out is that the EU ignores their own rules and laws. There is obviously significant precedent for this, so Scotland could promise to use the Euro, and simply not bother.