While it's good to have services like this even that I personally think they are already too many on Telegram, its users should not forget about the fact that usage of Telegram bots eliminate entirely the privacy factor while using them.
This is just a reminder that
Telegram bots, group chats and standard chats DO NOT HAVE ANY END-TO-END ENCRYPTION which makes all the chat logs stored on their servers and available to the Telegram law enforcement compliance team for further extraction any time later, without a need of employing any additional decryption.
The only communication channel on Telegram that enables end-to-end encryption is the feature called "Secret Chats", which is only available for person-to-person chats and is not even available in their official desktop app since the project launch.
Thereby, I suggest OP to make a SimpleX Chat bot instead, which would guarantee privacy by full and default end-to-end encryption of the data transmitted between it and its users.
SimpleX Chat is available on F-Droid which is another good security factor that guarantees users get app builds without any source code modifications during build process (this feature is called "reproducible builds" and it's a very important security feature since very few Android app users build binaries from sources themselves).
It seems you have a good rate, I remember an exchange where I spent 5% fees which felt too much.
In case that exchange guarantees no risks associated with suspension and confiscation of your funds and specially given the untraceable currency you get, 5% is a reasonable rate, given that using most exchanges nowadays represents risks of losing 100% of the amount where they could ask you for SoF, KYC and other nonsense and even refuse to return your funds later. You've got a great example of this
here.
By the way, I am yet to find policies in regards to risk screening of incoming transactions by the OP's service and therefore here is my question to the OP: what are risks if somebody sends 50 BTC coming from OFAC-listed address to your service? (I have provided an example with maximum risk so we can get straight to the point)