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For the first two requirements, please take a look at the following blog posts:
Products module: Adding and removing meta fields
Products module: Reusing Views
Products module: Adding new features to Generic Content module
Products module: Insert / Edit templates control guidance
What you should do after you add those additional metafields is to develop new views for managing the collections of those new meta fields. You should create tables and data classes that will store a collection of market places and colors available in your database. Then in those views you should use some logic for dealing with the CRUD operation to maintain those collections.
Then in the Insert/Edit templates for new product items you will add some logic for binding these collections of market places and colors to some web controls for visual display (dropdown lists, check boxes, etc). And then subscribe to the click event of Create/Save button to save selected values to the metafields using the ContentManager.SetMetaData() method.
As for removing the Description. You should first remove the Description metafield from the web.config and then remove the controls with ID="Description" from the Insert/Edit control templates.
All the best,
the Telerik team