Hi,
will be glad to work on your project,
I have a great experience in working on odoo with all kind of work, website, point of sale, backend, server issues, i am also able to alter the default behavior of odoo, to show specific options, such as a
*) new buttton for any specific task on list view
*) hide search view/group by/filter options from a specific view.
*) add calendar like options (day, week, month) in list view.
*) add qrcode in point of sale receipt to show any information required.
*) api integrations such as google maps, uploading attachments directly to google drive or alfresco.
1) the invoices can easily be send to an external web service as long as it provides api's for uploading data,
otherwise we need to make it able to receive files via api.
2) The invoice can also be printed in a special format.
3) gui will also be made.
the time provided is the maximum required, can be done in less time.