Hello,
I must admit I'm not sure what is that you wish to accomplish, but I'll try to answer the best I can.
First of all - if you want to create a contact using some of the values from a Company, you can add a contact by going to the selected Company and in Contacts addon click "Add new". Then, atop the screen you can see the "Paste company info button". That will take care of handful of fields, like address, country, etc.
As for the Sales Opportunities - in the default installation the only field related to customers is the Customers field alone. There's no other common fields between Sales Opportunities and Contacts.
If you wish to have defaults set for selected fields - that's entirely different matter. Currently, there's no other way but to code in new defaults. We have plans in the future to improve that system, but it's not very near future.
Kind regards,
Arek