The Thing About Disclaimers
Your plan to disclaim any connection with the actual character seems unworkable. First, disclaimers -- where someone attempts to disavow legal responsibility -- rarely provide a shield unless they are sufficiently prominent, carefully worded, and are in close proximity to the thing you're trying to disclaim. In some cases they create more confusion and in other cases they serve as an acknowledgement that you knew you were confusing consumers. Second, there is the practical application: for example, do you show up at the birthday party and tell all the kids that you're not really affiliated with the Harry Potter franchise? The Dear Rich Staff is not sure how that would go over -- probably something like this. In any case, offering the lookalike services for free would still be an infringement.
How Do Others Get Away With It?
Some people manage to get away with infringing activity usually by staying so low on the radar that the copyright owner isn't aware of them, or if the copyright owner is aware of them, the owner (a) doesn't consider them big enough fish to fry, or (b) doesn't have the resources to pursue everyone. (Photo shows the Dear Rich staff with one of our favorite licensed characters, the lovely Strawberry Shortcake).