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There is no real need to use all those domains. Build the trust and authority with your primary brand URL. Maybe use "some" others if there is any real value but 500, jeeze!!! That will be a ton of work and I think you'd be spreading yourself too thin. The best plan of action IMO is to focus on properly optimizing and building the TRUST for the company's branded URL. Forget all that old school "microsite" nonsense