Selling admin has always been considered disastrous and stupid, don’t be blinded by greed.
Making money of a server is far from easy, and if you make that your primary goal your server will never get off the ground.
Focus first and foremost on developing a good player experience(something which is practically impossible with moronic admins, unavoidable if it’s purchasable). Add custom content that attracts players, rather than offering something that can already be found elsewhere.
And if you’re going to be restricting content to donors, then only restrict custom content(that you or one of your developers have created), not existing or downloadable content(e.g. PAC).