IMO, cartridges are handy and usually faster than a pump, but I wouldn't head out with just carts. Sooner or later, you will more flats than CO2 carts I use CO2 on my "go-fast" bike, but I carry a small pump as back up. My other bikes have slightly larger pumps, and no CO2 inflator.
I would buy a small pump to start. CO2 can always come later