Do you need a public blockchain? The answer is almost certainly no. A blockchain probably doesn't solve the security problems you think it solves. The security problems it solves are probably not the ones you have. (Manipulating audit data is probably not your major security risk.) A false trust in blockchain can itself be a security risk. The inefficiencies, especially in scaling, are probably not worth it. I have looked at many blockchain applications, and all of them could achieve the same security properties without using a blockchain­ -- of course, then they wouldn't have the cool name.
https://www.schneier.com/blog/archives/2019/02/blockchain_and_.html