Your expense report isn't added to your invoice till the invoice is saved—that means if you attach the report during creation and then delete a line item before saving, the report will correctly have that expense entry removed, as well.
Product or service details: Specify Description, Quantity, Rate, Amount and Subtotal. The more details you include on the invoice, the better. This way, your client will know exactly what they are paying for upon receiving the invoice. Make sure that your client can understand every item, so that as soon as they receive the invoice, they can pay you instead of asking questions and delaying the process.