Model Railway Forum

You can of course often connect a Booster to the main DCC console and just use it solely as a power increase for the whole system e.g. a 1.5Amp DCC system can be Boosted to say 5.0Amps output. But its more normal to use the Booster to feed a dedicated separate section,

If it’s essentially a double track layout of approx 120 metres total track length with bus supplying every piece of track with a max of four engines running would the NCE cab controller have enough grunt?

Personally I would see what happens. I assume its the NCE PowerCab you're using not the Power Pro. The PowerCab comes with assorted power supplies. Usually they rated at around 1.3 - 1.5Amp but it can have a power source of 2.0 Amp available separately.
Even with the lower current rating it should be able to power four or five non sound locos and at least three locos with their sounds On all at once.
You can upgrade to the NCE SB5 if wished.