Yup, that's basically it; it will keep producing as long as it has enough inputs and output space.
A very roundabout way of doing it would be to make a drone take the output and put it in a storage that has just enough space for the number of items you want, minus how many of the items can fit in the assembler. This way, when there is no more space in the storage, the drone will stop picking it up, so the assembler will fill up, and then it will stop when its output is full.