Asterisk installation for 50-70 users

Hi everyone,

Can you please tell me the suitable hardware for the Asterisk server. I need to know what are the prerequisites? I have one single public IP, and asterisk will be behind firewall for security purposes. I think one digiium card with 2 ports are sufficient. And the output of digium card will be terminated at switch. Afterwards, from switch to convertor (RJ45 to RJ11)… and then telephone lines. i want suggestions from you all as i m amateur in asterisk technology…

Many Thanks,
Sudhir Kumar Rana