An option to create at least one custom gretting should be a feature of QB online.

I too would like more control over greetings to my clients particularly on invoice and reminder emails.  I agree with @snoble405 that "Dear" is too formal.

The problem would be solved if I could use a place saver so that the client's name is automatically populated but [First] and {First} inserted into the body of the email aren't working for me - should I be doing something else?

I guess I will continue to manually enter greetings and client names above the prefilled part of my template.