I can provide some information with adding your transactions in QuickBooks Online (QBO), @RFBSDot.
Yes, adding your bank account to your QuickBooks Online (QBO) is optional. You'll just have to add all your income and expenses to your account manually.
You can create invoices or sales receipts in recording your sales transactions. Choose to create an invoice for a deferred payment. Use sales receipt if payment was made on the spot. See this article for detailed guidance: Understand the difference between invoices, sales receipts, bills, and statements in QuickBooks Online.
To record your expenses, you can choose to add them by entering bills, cheque, or expense. You can create a bill if you'll pay it later. For expenses to be paid immediately or that have already been paid, use a cheque or expense depending on how you made the payment. Refer to this article for more information: What is the difference between bills, cheques, and expenses?.
Here's also an article for more information on how to categorise and match online bank transactions in QuickBooks Online.
Let me know if you need further help with adding your transactions and or anything else, by leaving a comment below. Take care and have a great rest of the day!