Most of the questions are unfortunately not possible to answer, for users:
Does the platform require registration?
This is the only one you can actually check, but maybe the least important one. Even if a platform requires registration, it could be managed in a way that the individual swaps aren't stored, and thus privacy could be preserved.
What data does it collect and store?
Are IP addresses and transaction metadata logged?
If the platform has a proper ToS then you can check what it
claims to collect, log and store. But you can never be sure that it's true. The strongest way to ensure this is maybe that the platform gives a legally binding guarantee in their ToS that they don't store the data. But a simple "We don't store X" is not enough to really prove that.
Is the swap non-custodial?
This is often used in a misleading way.
If the swap passes through addresses owned by the platform operator, then it's custodial. Even if the funds are only a millisecond on the exchange's address before the payout is made. The exchange could go offline in exactly that moment.
The only non-custodial solution between different blockchains is atomic swaps. Even THORchain is custodial, however there are strong incentives for the validators not to misbehave.
I don't question you're probably a reputable platform, but complete trust is not possible. There is no way to prove that the exchange hasn't logged or stored data.