With router series support routing the whole internet?
1) I think you need an EMI = ip services to run BGP on the C3548.
The device should be fine if you accept just two default routes, if you think to receive more you should look at something different with more capabilities in the signalling plane (cpu, memory to host a full BGP table)
2) there are several configuration examples
you have your own AS so you have your own public IP prefix(es)
3) probably some changes has to be done in order to secure the device.
at least an access-class to block access from the internet, usage of non default snmp communities and so on
Hope to help