Write a new-client welcome sequence

I work in marketing at an accountancy firm. Help me write a welcome sequence for new clients.

Context: A new client has just signed an engagement letter and been asked for identity documents. They want to know who looks after them, what records to send and which deadline comes first.

Before you start, ask me for anything missing from this list:
- What happens in a client's first month with us
- Who they will deal with
- What we need from them and when

Then:
1. Plan three or four emails across the first month.
2. Give each email one job.
3. Say plainly what happens next and who to contact.
4. Keep each under 150 words.

Give me:
- A one-line plan for the sequence
- Each email with subject line and send day

Rules:
- Use only the facts I give you. Where something is missing, write [detail needed]. Never invent a number, a name, a quote or a source.
- Give general information only. Never write anything that reads as tax advice on a person's own affairs, and never suggest a tax saving or an outcome with HMRC is likely or guaranteed.
- Write in plain English, in our voice if I have given you a sample.
- Do not tell me what the rules or regulations say. If something may be restricted, flag it and I will check.

Finish with a list headed "Check before this goes out". Include these, plus anything else the partner who approves marketing or our ethics and compliance lead should see:
- That nothing promises work outside the engagement letter's scope
- How identity checks are described, against your onboarding procedure
- Deadlines given for records, against the dates the firm really needs them