Hi Liz - Generally you do it in this order:
Import customers & suppliers
Import customer Invoices & supplier bills
Import bank transactions
Import any opening TB by importing a journal entry.
If all you need to do is set up customers and suppliers names, without all the other standing data, like addresses etc, then you can skip the first import as importing the invoices & bills will set these up for you. Not much help though if you decide to go ahead with CB, as you then have to setup the contacts' standing data manually.
If you are importing historic invoices & bills that have been paid off by bank transactions, there's an Import "Sales payments" and "Bills payments" where you just list the inv/bill number, date and amount and they pay off the invoices/bills, you can then import the other bank transactions as normal.
Hope that helps?
By the way, there's a video on other, non-numbers setup you might find useful:
https://youtu.be/Y0kZ-fJKTNE