Tos8
I think if I were you, I would take the earlier appointment whilst awaiting the later appointment with the person you would prefer to see. ultimately that way, if you aren't happy with the fellow, you have lost nothing but have at least been seen earlier. You still have the option to see the other guy in Feb.

Given what you have said, its much more likely to be your pre-existing hypertension that is the cause of your kidney issues. Your blood pressure problem from childhood is a classic cause of the kidney condition you now seem to have and much more likely to be the cause than CRPS. That's not to say that your CRPS isn't a complication in the picture or relevant to your treatment but your other medical history is a very common ans well known pre-cursor for the situation you are in now.
Best of luck with your appointments.