First of all, thanks for the clear post and background. I do believe this is in the correct place. Also, I'm not an expert in design, so please take my opinion with a grain of salt.
The problem with having both "Close" as "OK" is that people don't believe data disappears: they type a new number somewhere and, if they press Close instead of Cancel, will expect that number to sink in with the application. "Close" is implementation--it says the window will close, but gives no other clues (i.e. will the application accept my input?). "Close" is either OK or Cancel; in your case, it seems to be Cancel, so my advice would be to label it such.
4 buttons is not for the average user. However, the buttons you have each serve a clear purpose, so you don't have a problem, in my opinion. Other than "Close" > "Cancel", your labels seem fine to me.
Perhaps someone more knowledgeable can give a more authorative answer.
Your use of this web site or any of its content or software indicates your agreement to be bound by these Terms of Participation.
Copyright © 2015, Oracle and/or its affiliates. All rights reserved. Oracle and Java are registered trademarks of Oracle and/or its affiliates. Other names may be trademarks of their respective owners.