If you want that first email to go out immediately, you should include Email 1 as part of the Entry trigger.
see
https://www.slideshare.net/jdavidhill/master-nurturing-and-marketo...
If you can't use Contact Roles, you need an Account or Contact level field identifying an opp.
Has Opp filter has Record Type or Opp Type filter (or you can add it in SFDC).
You may want to read SFDC docs on Formula fields to accomplish this.
If you look at Account scoring guides, most don't recommend this approach anymore.