If your clearnet website has been under almost continuous DDoS then most probably the only beneficiaries from would be competitors. You have only recently launched your business and it has already been coming under sustained DDoS.
From a business perspective, having any donation based as a sole source of income at the core is something not recommended, while many have succeeded many have not ( and I am not referring to wider business not mixers).
As you have increased the optional fee to 0% it should act as a mechanism for users to increase anonymity as they mix in greater numbers increasing deposits but with that being said I would expect the subsequent 3 months of trading to bring you very little (if any) income via transaction fees.
There is only one way to find out if the optional fee could work and that is to try it out for a while. 3 months is a decent timeframe and should be more than enough to convince ourselves if this is viable or not, and even if it's not the money would not be wasted as profits are not the only goal of this trial.
At worst after 3 months we lost a bit of money, but the anonymity set and security of the entire service will be so strong that there won't be a single reason that would make it worth it for someone to use a competitor instead of us. You would get provable and undeniably better privacy at a much lower price.