Invoicing as a sole trader is simpler than most templates make it look. There is no Companies House number to quote and — unless you are VAT registered — no VAT to show. What your invoice does need: your name (and trading name if you use one), your address, the customer's name and address, a unique invoice number, the date, a clear description of the work, and the amount due. That is the whole list. You do not need to put your UTR on invoices, and you should never put your National Insurance number on one.
Both work. If you trade as "Smith Property Services" you can invoice under that name, but your own name should appear too — clients are paying a person, and their bank may check the account name matches. The generator's business name field takes whichever format you use, and remembers it on your device so invoice two takes seconds.
HMRC expects invoice numbers to be sequential and unique — not random. The classic sole trader mistake is starting at 001, losing track, and issuing two invoice 007s. InvoiceIt numbers sequentially and keeps count on your device, so the sequence looks after itself. Keep copies of every invoice you send; they are the backbone of your Self Assessment records.