Here are some URL for the cat6k spec and datasheet
http://www.cisco.com/en/US/products/hw/switches/ps708/products_data_sheets_list.html
http://www.cisco.com/en/US/products/hw/switches/ps708/index.html
There are many types of GBIC modules that you can insert, plus you also have to decide, you do you need redundant supervisor or single supervisor. Generally the GBIC comes with 16 port at the max per module. Also you do need any ethernet module.
You do you need to find out if you need 1000 copper ports or fiber ports
Also you can also look into Cat4500 series switches if you need only simple routing.
hope this helps