I've finally realised what a good parting out process is.

First, add the sets into your store. This leaves your stock for sale even if it takes you years to get around to parting the sets out.

If you're running out of storage space, deboxed LEGO stores in a half to a third of the space of raw LEGO sets. Debagged LEGO stores in a smaller space still.

When it comes to parting-out time, if you must sell boxes only sell a handful. There's really no demand for the things, they're heavy and they take up space. However, they are handy for use as mailing boxes, when turned inside out - especially the smaller ones. The bigger ones just weigh too much compared to specialty mailing boxes.

Print out the inventory so you know what extras and alternatives there are in the set - set those aside as you encounter them. Any other parts can immediately be added to physical inventory.

The distinct steps in parting out are:

1. Debox: Separate the instructions and other loose parts of the set out and store them, group identical bags together. One time-unit.
2. Debag: open identical bags, pour into a big container, extract small parts bag and do the same for that. Two time-units.
3. Sort into individual lots. Two to four time-units.
4. Add to BrickLink inventory, including counting extra parts. One to two time-units.
5. Ingest into physical inventory. Two time-units.