Hi,
well then it's a good idea to create your own page for the web service. I would only put the fields you need there. A page web service doesn't care about visibility of fields, only the order is important, as it's validated in that order. To get the full functionality, you would also need to enter a password (for username/password authentication). You can add the user property table as a page part (you need an own page for this) in your page.
With the User Card page as it's designed I'm afraid it's pretty complicated to get the webservice call right.
with best regards
Jens