Text input field in chatblock - label and admin-defined length?

Would it be possible to add a label to the text input field, something like "Type your message here"?

The text field in the chatblock is also very small, it would be nice if it was an admin-defined length, and I'd love the ability to make it a multi-line textfield... small text fields are fine for idle chatter, but I'll be using this in a business context so users will appreciate ease of review before clicking Send!