Yes, you can have multiple people entering invoices. The numbers are assigned in sequence.

Contact your dealer re pricing or look up a dealer in your area here.

Sometimes using "archived invoices" as templates can speed up the process. If a large proportion of your invoices are similiar with only the qty/hours changing, you can restore from an archive batch, changing the customer number and updating the invoice number. Then you may only need to modify the qty/hours and the new invoice is finished.