Hi Lim,
Kindly check the below links, you should use VIP2-40 or higher, up to four T3 ports can be operated simultaneously on each VIP (up to three T3 ports per VIP2, with each port running at T3 clock rate, while up to four T3 ports per VIP2, with subrate clocking enabled).
The only constrain with the 7500 router is aggregate bandwidth for the dual CyBus, you should consider this when populating your router with VIPs - the Cisco 7507 has two CyBuses (called the dual CyBus) for an aggregate bandwidth of 2.134 Gbps (1.067 Gbps each), the 7507 dual CyBus has seven slots: interface processor slots 0 and 1 (CyBus 0), RSP slots 2 and 3, and interface processor slots 4 through 6 (CyBus 1), you must consider this when populating your router (you should consider this issue mainly if you've installed a GigaEthernet interface).
As for the cable you should use CAB-ATM-DS3/E3=.
Cisco 7500 Series Installation and Configuration Guide:
http://www.cisco.com/en/US/products/hw/routers/ps359/products_installation_and_configuration_guide_book09186a008009c1bb.html
Packet-over-DS3 Port Adapter Modules
http://www.cisco.com/en/US/products/hw/modules/ps2033/products_data_sheet09186a00800a3e07.html
BR,
Mohammed Mahmoud.