First ever invoice - Detailed to include

Hello, I want to make sure I include all relevant details on my first ever issued invoice. I have searched information and found https://www.gov.uk/invoicing-and-taking-payment-from-customers/invoices-what-they-must-include very useful. Am I correct in thinking that I don't need to include a UTR in my invoices? Since I have never received income as a freelancer yet, I don't have a UTR, however someone told me I would need to include this in my invoices as a self-employed, and I see this is not listed in the above searched page. Additionally, can I create an invoice by hand, as in using Microsoft Excel and not a business software platform? I don't own an accounting platform because the job I am going to do as a freelancer is casual work and not relevant-high income. Finally, I don't know if invoices are given reference numbers in any special way, or if they need to have a specific number of digits. Shall I number by first invoice as "#1" please? Many thanks!

Hi
Please look here for the types of records needed as a self employed trader , Business records if you're self-employed