You shouldn't use goto. What you showed can simply be resolved with simple if statements instead.

Code:
on *:join:#: {
  if ($nick == username1) msg # custom welcome message 
  elseif ($nick == username2) msg # custom welcome message 
  elseif ($nick == username3) msg # custom welcome message
  elseif ($nick == username4) msg # custom welcome message
  elseif ($nick == username5) msg # custom welcome message
  elseif ($nick == username6) msg # custom welcome message
  elseif ($nick == username7) msg # custom welcome message
  else {
    if (%floodwelcome) || ($($+(%,floodwelcome.,$nick),2)) { return }
    set -u10 %floodwelcome On
    set -u99999999999 %floodwelcome. $+ $nick On
    msg # Hey $nick welcome to the stream!! hope you decide to stick around and hangout for a bit, and don't forget to follow if you're enjoying the stream!
  }
}
Just don't make a habit of using goto, it's very unreliable and there are easier ways to do what goto offers anyway.

Personal opinion: I would just make a ini file that stores all user's messages. Would reduce the code length and would offer more convenient edits to it. Want me to show you how it works?