The company itself
Name, country, industry, entity type, base currency, and when your fiscal year starts. Then a Chart of Accounts template — US Small Business or LATAM Small Business. It is a starting list of accounts, not a cage: add and rename freely afterwards.
Entity type matters more than it looks. It decides which tax strategies apply to you and how some reports are laid out.
Then, roughly in this order
1.Settings → Branding — your logo and colour, so documents look like yours before you send one.
2.Transactions → Connect bank account — the books fill themselves from here.
3.Customers — add the ones you invoice regularly, or let them arrive as you go.
4.Accounting — glance at the chart of accounts and rename anything that is not what you call it.
5.Send one invoice. It is the fastest way to find out what is missing.
What can wait
Payroll, inventory, projects, the virtual assistant. None of them make the first week easier and all of them make the first day longer.