If you want to disable the default payment gateways but still insert orders into your database, then you can just set this variable in the WA_Globals.php to true:
$WAGLOBAL_Test_Mode = true;
this will not use any of the default gateways when going through the check out process, but it will insert the order and order details in the database.
But if you are looking to implement your own gateway, then on the confirm page, you will need to remove line 997 - 1110 (or just comment it out).