Your electrician needs to install your whole house breaker, and he will know what will fit your panel the best, and also what he has easy access to.
As far as power distribution, most rack manufacturers will be able to supply you with plug mold that clips to the back of the rack, so you don't take up rack space, and the power is at the rear of the rack where it needs to be.
Like this.
Who is the manufacturer of your rack? My three racks are Middle Atlantic by Legrand.