Hi,
Personnaly I agree with Alex, I dont think fees for payment using own gateway is a good idea. Zero fees for payment should motivate users to use this payment method. Anyway, it depends on your business model, and having aditional options in the extension is always a good thing.
Actually, for second option of multi stoe that Alex mention, wc marke tpace is fine, i tested it. As it’s woocommerce based allows payments with this extension, but payments to vendos must be in fiat money (because in their dashboard there is no integration to choose payment from this gateway with crypti). The only thing I can think at this stage is about the risk for admin of loosing money due to fluctuations in crto/fiat when the payment to vendor is made lately according to payments admin settings, but it’s something regarding the site operator. Maybe this problem could be solved by an additionnal option af sharing the risk (or the positive earnings if change rates were positive).
Regarding fees, it would be good implementing some tab in core extension in order to show total earnings from transactions for admin.
Best regards