Hello,
I have been working on a solution to this issue that will allow you to easily set minimum withdrawal amounts. Additionally it will be possible to specify withdrawal and internal fees in detail per each coin (both fixed amounts per transaction, and proportional to the transacted amount). The plugin will start off with the same values as those used by the CoinPayments platform, and the admin can then increase these values if needed.
As a sidenote, I do plan to implement a maximum withdrawal amount, but I plan to do this differently, as part of the parent plugin. I would like the admin to be able to say that a user can withdraw up to the equivalent of X USD per day, and the total will be over all types of currencies. I believe this is more useful as a safety precaution.
I will notify you again here, when the solution I’m working on is out.
with regards