Let me share some clarification about indenting the line description.
Currently, an option or keystroke to indent text in forms is unavailable. As a workaround, you can go to the Description box, then click the space bar before you enter or paste the description. Another method is to copy the indented description, just like what you're doing.
I appreciate your input on this feature, and I'll make sure to let our product engineers know about your suggestion. We always update the features in QuickBooks Online, and this preference might be added in the future. As we assess this, I suggest you visit our QuickBooks Blog to stay updated with all the changes that are being made.
Also, I've attached some articles you can use to email and personalize sales forms in QuickBooks: