Do I need a common mode choke at the feed point (transformer)?

No,  the transformer itself has enough common mode isolation impedance (5000-19000 Ohms) so additional choke might have an impact on transformer primary winding and make an impact on antenna tuning.  We do not recommend any chokes at the feed point especially coiled coax chokes which actually might increase common mode currents on any antenna feedline. BUT we strongly suggest installing the CMC at the entrance of your cable to the home in order to prevent any induced RF or common-mode noise signals to enter the home and interfere with your station and appliances. Note that all cables entering homes must be grounded before entering the home and CMC should be installed between that grounding point and antenna. See Grounding links in our tech library.