Cheers. I hope someone else is reading this too. 
1. Yes, us too (20 in the team). We’ll use email for that - not all email personal email accounts are linked to HS in our case.
2. OK, I wasn’t sure how you would deal with incoming attachments. I understand how that could be managed for outgoing. That said, the absence of useful permission in the file system may not help on the privacy aspect.
3. Ah, OK. We don’t use HS CRM as our primary CRM so don’t have that point of view. Even in Salesforce we don’t normally have anything client facing that can’t be open to the team. If there is, we keep it in email or permission governed shared folder location.
4. I had inbound attachments in mind.