Ask HN White-Label service: How do I go about it?

I've been asked by a client to create a White-label service similar to an existing product I have. The service will have the client's logo on it. The customers they bring to the service wouldn't be customers I would get to my service so I'm not losing out. I will host the service and they will point their customers at it.

Questions:

* Is it okay to charge for development costs when enhancing your own product?

* Is it okay to put a link on the white-labelled site such as "powered by mycompany"?

* What is a typical revenue split when providing a white label service?

* Or would it be more typical for me to charge the client a fixed monthly rate and they keep the revenue from the clients that use the service?