It's a good ideal, but not a must. The reason for all the items being in the tank and filters is so that the bacteria bed will be larger, but the bed is going to be as big as the amount it takes for your fish. If you can't put them in now, it will still be fine and your tank will still cycle. When you add the new things they will build up a bed on them also. Just when you add your fish don't put in 30 right off the bat and you'll be fine 
Better to have them now? Yes
A must? No
Better to have them now? Yes
A must? No