3. "I chose 0.1BTC as a trial, but when I complete the transaction, the final invoice shows the minimum payment as 0.00022BTC instead of the 0.1BTC I use for exchange." :- It show minimum payment to address below this if user send coin it will refund. That was minimum amount you can start exchange on our platform according to pair selected.
Sorry, but this doesn't make sense. In all other exchanges, the exact number you chose for the exchange appears with a message telling you that you have to pay the exact amount, otherwise the transaction will not be accepted.
In the above example the user tried putting 0.1BTC this means that a message should appear on the final invoice telling him that he has to pay exactly 0.1BTC to the address on the invoice.
If the user pays a wrong number to this address, how will he be able to get a refund? How will he be able to prove that he sent the amount to the specified address?