1. they dont have to be ceramic all round but it is recomended (just change them as the way you go)
2. Yes disc machining is generally a good idea when your changing pads regardless though with the ceramic pads you would want to upgrade the rotors to something stronger than OEM as ceramic can eat through the rotors pretty quickly when pushed
3. Yes Ebay readstuff is cheap and they are genuine, they are cheap because they dont not have store upfront cost and stock holding fees
4. A lexus mechanic is still a lexus mechanic if they can do a brake change on a normal car then they can do it on a lexus