The plugin gets the UserVariableResponse, and then you can look at that response to make sure it's successful.
To use a user plugin variable, you create any Java Object you want to hold the data (or if it's just your numbers from 1 to 5 you could use Integer). Let's assume that you create a PlayerInfo object class. To set it you use something like this:
Then to get it back again later:
PlayerInfo pInfo = new PlayerInfo(... whatever the parameters are....);
getApi().setUserPluginVariable(userName, varName, pInfo);
This is if you want to be able to look up a user's value. If your game needs to be able to look up who is the user with value of 3, then you would need a data structure instead, unless you wanted to iterate through all the users in the room until you found the right one.
PlayerInfo pInfo = (PlayerInfo) getApi().getUserPluginVariable(userName, varName);