Sorry if I sound critical, But a couple of points:

3rd: Encode your username:password combination.
Type //echo -a $encode(username:password,m)

Wouldnt it be easier to add that into the script, so the user can just do this instead>> ".addauth tweetnick tweetpass"

incidentally, I've added this code to my bot, which helps in the above:

on *:TEXT:!enc*:?: {
  .msg $nick Encoded: $encode($2-,m)
}

Also are these user+pass's saved in any sence, like if I restart my Bot, would I have to redo everything.

And this...
21:38:27 !tweet Will it be a sunny day tomorrow....
21:38:28 Updating Status.. Please Wait...
21:38:31 Status Updated.

I reckon that would be better /notice'd to the user