Great summary!

One note of correction regarding W-9 and W-8 forms: Those forms are only required if your company intends to pay United States taxes. If your company is located outside of the United States and you have absolutely no U.S. presence (so, no equipment, employees, operations, etc.), that form is not required.

We often have U.S. customers ask for our W-9 and they are sometimes confused when we explain that companies outside the U.S. do not get dinged by their I.R.S. Referring those customers to check with their accountant if they remain in doubt has always cleared things up.

In Europe inter-bank transfers are free (unless there is a currency change) which can make them a better option than checks as they are quicker.