How much could I probably sell this for? And is this description ok?
Use Ebay as a market research tool.
Search for your item/s, 'Duel Masters cards' and see what comes up.
Then you will know what's hot and what is not
You can also, do an 'advanced search.'
The button for it, is to the right of the search button.
Then in the menu, click the 'completed listings' option, and you can find out final prices etc.,