1) I wouldn't recommend using a non-terminating timer that is set for 30 seconds for your nick change. As an IRCop on a couple of networks, if I saw that I'd be asking them why they are changing their nick that often.

2) Since you have different passwords for each nick, you're going to have to store the passwords also. This can be done in the nick.txt file by altering the format to <nick> <password>
Note: the <> should not be included.

3)
Code:
alias nickchange {
  inc %z
  if %z > $lines($mircdirnick.txt)   %z = 1
  var %newnick = $read($mircdirnick.txt,%z)
  .nick $gettok(%newnick,1,32)
  .ns identify $gettok($%newnick,-1,32)
}

Again, use this code with the timer at your own risk.
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