In the options (alt + o > Display > options > tray), check the box "on startup place mirc in tray" to have mirc in tray on startup.
To open the script editor on startup, you can use the following code:
on *:start:s_editor
alias -l s_editor .comopen a WScript.Shell | .comclose a $com(a,SendKeys,3,bstr,% $+ r)

Looking for a good help channel about mIRC? Check #mircscripting @