Welcome to the Forum, Peter.
Laptop, phone, travel expenses, to name but a few
When dealing with foreign VAT buy some hours of explanation services from a bookkeeper with experience in that field. Explaining this in a forum post is not likely to come across well.
That's highly unlikely. VAT is usually a zero sum game. If you import services or goods from SA you are paying the VAT directly to the Dutch government. Not through the invoices of your SA partner.
What your options are and if your choice of the Eenmanszaak is the best, that's impossible to be definitive about. It probably is, but there are plenty reasons to not choose an eenmanszaak