When assembling a toy, you can order the parts piece by piece, or you can order the entire toy together. The better option is to order the whole toy together. You can only have a limited number of open orders at the same time. However, ordering the entire toy at once counts as only a single order. Ordering individual parts can be done in situations where after a quest a character will give you a toy back with a broken arm or leg. In this scenario, getting spare parts is cheaper than re-purchasing an entire new toy.