I think you have answered your own question.
Leaving the compressor off the robot is your option. This is no option to leave the primary pressure valve off. the primary side pressure valve with the gauge is required.
And I think if you showed up at a regional and tried to charge your tank with anything other than the FIRST supplied compressor, you would be swarmed by nearby mentors, judges and inspectors!
(the FIRST supplied compressor will not put out more than 120PSI max).