Welcome Email

I have my clients purchase packages through my website. Once the purchase is made, I would like to be able to send a Welcome email from Design Files with a button to fill out the Project Questionnaire.

As of right now, if I go to the project and request for them to "update" the questionnaire they just get a button that says Fill Out Design Questionnaire and it skips over my custom Welcome message that I added to the Questionnaire. If I add the custom welcome message to the "Update Questionnaire" request and it just looks bad…more like a screen shot of a message than a formal looking email. (see attached image)

If I try the "Invite Clients By Email" option, it could work if all the fields were customizable, specifically the button text. Also, the preview when you are editing the email does not show what it actually looks like? (I have attached pictures below of the preview/edit view in DesignFiles and then the actual email) That can be confusing.
I'd like to be able to change/see the actual font style on the header in edit mode, I'd like to customize the text on the button that currently says "Request A Project" (I'd like for it to say Get Started ideally), and I'd like the justification to be changed/viewed. In the edit mode it only shows at centered.

I could probably figure out how to do this through a marketing email from my website, but it would be easier to have an option directly from DesignFiles.

Thank you!