The TO/GA button also works with the AP. Ive set two buttons on my joystick so I'll hit the TO/GO button then shortly after takeoff I'll engage the AP. The plane's pitch and roll modes come on and the plane continues to climb staight ahead, 10 degrees pitch up. Then I know everything is good to go while I set the AP over to whatever modes, headings and other settings I need.
I went into the xplane key bindings and set the B key to toggle brakes regular. You could also set a key or joystick button to toggle maximum or press to hold for braking action. If you have a driving sim setup you can also use the driving pedals as right and left toebrakes.