Using AppleScript to toggle Internet Sharing not working
You can use this code to activate sharing with settings which were already there:

tell application "System Preferences"
    activate
    set current pane to pane "com.apple.preferences.sharing"
end tell
tell application "System Events" to tell process "System Preferences"

    --find lock and click it if it is not unlocked
    repeat with x in buttons of window "Sharing"
        try
            if (value of attribute "AXTitle" of x) is equal to "Click the lock to make changes." then
                click x
            end if
        end try
    end repeat
    delay 5

    --find the checkbox for Internet Sharing and select the row so script can enable sharing through ethernet
    repeat with r in rows of table 1 of scroll area 1 of group 1 of window "Sharing"
        if (value of static text of r as text) starts with "Internet" then
            select r
        end if
    end repeat
    delay 2

    --enable Internet Sharing
    repeat with r in rows of table 1 of scroll area 1 of group 1 of window "Sharing"
        if (value of static text of r as text) starts with "Internet" then
            set sharingBool to value of checkbox of r as boolean
            select r
            if sharingBool is false then click checkbox of r
        end if
    end repeat
    delay 2

    if (exists sheet 1 of window "Sharing") then
        click button "Start" of sheet 1 of window "Sharing"
    end if
    delay 2

end tell
ignoring application responses
    tell application "System Preferences" to quit
end ignoring


Hope this helps!