When you create invoice manually then conform and follow below steps :

  ->  Taxes and payment terms you have to set in related customer that you have selected in invoice.

  ->  Invoice date will be set automatically when you click on validate button, it will not set automatically in draft state (means at time of creation)

  ->  Invoice Number will be set automatically when you validate invoice, for invoice number if you want to see in detail can go in  Settings -> Accounting -> eInvoicing & Payment. In that you can see Next Invoice Number (for both supplier invoice and customer invoice).   and for more detail you can go in Settings - > Sequences & Identifiers -> Sequences.

I got a 403 error when trying to edit message above. Here is a better overview of the imported fields:
 

Did you check the Subscription module of Odoo 9 Enterprise. It allows to manage contracts & plans and automate invoicing (as well as payments if you support credit cards).

In addition to automating billing and payments, it provides great dashboards for recurring business: mrr, churn, cltv, ...

We use this module to manage thousands of our customers with complex offers: monthly, yearly, multi-year, options, ability to switch plans, customer portal...

All you have to do is to import quantities to bill on each contract periodically.