Can you allow for a contact to be attached to an opportunity so you don't have to enter the contact again?. You should be able to add a contact to multiple opportunities as well.
You can relate opportunity to CRM Account (contact or company) using several ways.
1. When you create an opportunity, you can relate it to CRM account from creating form http://prntscr.com/h53smc . If contact or company is not found, you can create a new one.
2. On the page of existing opportunity -> http://prntscr.com/h53vfg
Customer support service by UserEcho