For your first question, the SEF URL needs to be generated first, so if you want the SEF URL to be created just after the registration, you will probably need to put the link to the newly created profile to the "Thank you for registering" page if you have it. Or modify the CB code to generate the link after registration.
Second question: If I understand it correctly, the problem is with losing POST values during redirection of non-SEF URL to SEF one. JoomSEF doesn't redirect URLs when there are some POST variables present, so this shouldn't be a problem.