You can sell to your heart's content.
However if it has a proper Arduino as its core as you say, and as you state you have done very little to make it your own work then calling it an Arduino could land you in some problems.
The best work around is to use the word "Compatible" after the name which limits your exposure slightly. As for using the LOGO and or other trademarks you may have issues.
Just emailing Arduino will not always get you too far.
You need to have a few things lined up such as schematics, product pictures, and a detailed selling plan before you contact them.
Just an email saying Hey I want to sell this board with a shield on top for doing "x" is not really a good idea as they no doubt get lots of those and there is only one place I know for them. 
I think @Per has worked on something that may also be of help.