Can I send emails to my users manually from storehippo admin?

Yes, you can send email notifications manually to your users via StoreHippo. You first have to add notification templates in Setting > Notification section of StoreHippo admin panel.  You can then, send the notifications manually to the users in Customers > User section of the admin panel.

For more details about how to send email notification, please refer:
https://help.storehippo.com/topic/send-notification-to-user