Hi @edev ,
I currently only have an answer to your first question. Right now, it is only possible to send an attachment with an email using the SMTP API. Sadly, you can not use the Single Send API to send an email with an attachment.
I’ve built a NodeJS app with Express that I use to send emails using the SMTP API for any mails that require an attachment. I use a workflow with a webhook to trigger my NodeJS app.
I am willing to share the code if you need some help.