The answer is it depends on what kind of services you plan to offer.....dial up, leased line, frame-relay, ATM, web hosting..........
but, for the basic dial in ISP you would need...........a remote access server, an authentication server, dns servers, mail servers, a dial in line to connect to the remote access server, and some kind of connection to the internet
Questions 2 and 3 are a little to in-depth and vague to answer in this forum