Knowing how many you need
I guess I'm like most players - that is to say, I have most jobs high level and to save space, I send my extra seals to another character. In this case, to remember what items I have and how many I still have to get, I've made a grid that I can simply print and note down all the items as I get them.
How to read the chart
In the first line you have the body part and the number of items that you will need to get for the upgrade. The first digit is for seals, and the second is for items+2.
Inside the table you have letters ABCD, just check the bottom of the table to see which item these refer to.