Bled the brake reservoir empty, what next?
 

Installed a front BBK with stainless steel lines and I accidently let the reservoir go empty. We kept bleeding and bleeding and there were still some micro-bubbles. I eventually eventually ran out of brake fluid and started to re-use some of the brake fluid as it was clean. I had 3 32oz bottles. The pedal is stiff but not as stiff as it should be.

Do I need to bench bleed the master cylinder? I was thinking of bleeding all 4 brakes with 1 gallon of brake fluid.

New rotors and brake pads? Go and bed-in the brake pads first and see if the brake pedal is still soft.

This, and make sure you get into the ABS to cycle the pump and possibly free other air that may exist

I made this mistake in another car once, had air in the abs pump.
Its a mess, but you have to "cycle" the abs pump to get the air out.
In my case i had to bleed the brakes every time i engaged the abs pump on some wet stretch of back roads. Honestly i didn't know any other way to do it and on the third time my brakes were back to normal pedal stiffness.

I installed the CTSV brembos on the front. After bleeding and ran the resevoir dry, and bleeding again until I ran out of clean brake fluid. I called it a day and bedded in the brakes where I activated ABS each time. I bled the brakes on all 4 corners a few days later and all the air is gone. Pedal is stiffer than stock with the SS brake lines :')