Thanks for your feedback. You can edit the fields upon your quotes and invoices using either the invoice settings, quote settings or pdf themes under the 'Settings' menu.
Your suggestion to add character names into the invoice number has been raised before, however this does lead to issues when tracking invoices within the app and the sequential reporting based upon invoice number.
Could I suggest using another field to hold this information if you do need to create separate invoices for a single case. You could use projects for instance to create multiple invoices for a single job, that can then be attached to the one customer.