I keep two spreadsheets, one to track the pen components that I have on hand by supplier, date purchased, price, style, and coating. In addition, I track number purchased, on hand and those used.
On the other spreadsheet I keep what seems to be standard information. I have an inventory that includes a pen number, date made, type and color of blank, pen components, and finish. I also have a suggested price on those for a guideline.
When a pen is sold, I move that pen information to another worksheet with the disposition, price, where and when sold. This allows me to track where and when the pen was sold.
This impressed a good customer when he asked for a pen from the same set of components that he bought 18 months ago. I have this on my computer and in Dropbox so I can access it from my smartphone. I also use dropbox to keep a public folder of pictures for those wanting to know what I can make for them or have on hand. I do not yet have a website.
This works well for me.