Even though you might consider yourself an advanced sewer, knowing every single detail about sewing shoes might be a bit out of your compiled (yet still very expertise) knowledge range.
The types of threads and needles that you can use with your shoe sewing machine will have a very direct connection with the type of material the shoe is.
If you’re working with leather, you’ll want to opt for bonded nylon thread—which can be found in various weights and thicknesses.