The rate limit for IP is a good option if it is high. Links to RPC should not be made public, on chainlist.org and so on, but only those who find it on the Tornado website will use them at most.
It will probably also require additional configuration to reject requests that are not native to Tornado - for example, calling third-party contracts or receiving blocks in a different way than is done in the Tornado Cash interface.
And I wait link to your to your domain for selling RPC access to prove your credibility.