Another option is to go ahead and keep him in his current cage since it is only going to be a little less than a week till the vet appointment anyway. Allow him time out while your getting to know each other over the initial first week of course, but at least this way you will have a cage that is easy to transport him in to the vet and not have to worry about it so much since the morning of the vet visit, you could simply just not let him out.