Email 1: welcome, on the day they sign
Keep it to five sentences. Thank them, name their bookkeeper and reviewer, say what happens this week and when they will hear next. Do not ask for documents yet; the client is still enjoying having made a decision.
Template: “Thank you for choosing [Firm]. Your bookkeeper is Fatima and your reviewing accountant is Rahul; both are copied here. This week we will set up your accounts on [Firm] Books, our client platform. Tomorrow you will receive a short list of what we need from you. If anything is urgent before then, reply here or message Fatima on WhatsApp.”