enabling/disabling Internet Sharing with terminal in mac osx 10.9.2
I was browsing the same thread you linked to and also found that none of the answers worked. However I was able to modify Philip Regan's solution to work with my Mac OS version (10.9.3).

Here is the modified solution.

tell application "System Preferences" to set current pane to pane "com.apple.preferences.sharing"
delay 1
tell application "System Events" to tell process "System Preferences"
    click checkbox 1 of row 8 of table 1 of scroll area 1 of group 1 of window "Sharing" -- change to row 10 if you are using anything before Snow Leopard
    delay 1
    if (exists sheet 1 of window "Sharing") then
        click button "Start" of sheet 1 of window "Sharing"
    end if
end tell
ignoring application responses
    tell application "System Preferences" to quit
end ignoring


This pertains to number 2 in your list... you might want to check out an app called "Accessibility Inspector". It was helpful in finding the new path to the particular GUI element this script modifies.