Would be handy to have Invoice Notes template, that can be set into the Templates section, then, select the one you need when invoicing.
For instance, you could add under notes the payment procedure, payment time frame, payment option, payment details, as well reference number (as ticket number) so the payee can include the ref. number when making the payment via bank transfer.
I`m using 2 types of notes, one for local currency invoices and one for Euro invoices,
And have the footer note just with the company`s details: name, address, contact, company reg. number, email and web address