Hi,
In order to do Enterprise Database picks (ODBC as you mentioned) and TTS, you will need the Premium package. You will need a separate TTS server such as Nuance or WebSphere to integrate with UCCX. You will also need a database to connect to over ODBC (but I assume you have this already).
You can probably get away with 15 - 20 seats depending on how you will use the system. The licenses are consumed as per page 33 of the following document:
http://www.cisco.com/en/US/docs/voice_ip_comm/cust_contact/contact_center/crs/express_7_0/installation/guide/uccx70ig.pdf
