Who can explain is it possible to use minimum residue minexcoin that I must maintain on my balance for parking?
No, it will be impossible to park coins which is on card balance. But it's very easy to top up it from your wallet. MNX network is enough fast.
So it will be not possible to sign message from card balance address? Is this address will be under control of minexbank or some application like that? In another case I can park coins if sining mesages is possible.