At booking we only ask for a name and an email or phone number. After that, each message asks one small, optional question at a natural moment - what they are looking for, designers, sizes - so a client record builds up quietly over time, without a sign-up form. On the right is the record you would see filling in.
Answers would sit on each client's record in Shopify, so you could use them in emails later, for example to tell someone when a designer they love comes in. Before building it we would check what Cowlendar's booking form can do and agree with you which tool sends the reminder and thank-you messages.