Re: ground bar
408.21 is for grounded neutrals, not for equipment grounding conductors. see 110.14 below, this would cover equipment grounds as well as neutral conductors. I have seen on the legend of some electric panels where they allow you to combine equipment ground conductors but they do not allow you to combine neutrals or grounded conductors. I have seen C. T. cabinets & switch gear that have the terminals listed & labeled for 2 wires in one terminal. (neutrals as well as hot wires)
110.14(A) Terminals. Connection of conductors to terminal parts shall ensure a thoroughly good connection without damaging the conductors and shall be made by means of pressure connectors (including set-screw type), solder lugs, or splices to flexible leads. Connection by means of wire-binding screws or studs and nuts that have upturned lugs or the equivalent shall be permitted for 10 AWG or smaller conductors.
Terminals for more than one conductor and terminals used to connect aluminum shall be so identified.
Greg