Copy products for eBay & eCommerce sites to Magento

We have approx. 400-600 products (could be more) listed across eBay (2 Sites listed with SixBit and Marketplace Advisor), a CS-Cart, BigCommerce, Marketplace and a oscommerce based website that we need copied across into a multi store magento site. There will also be a list of products in excel will be provide that will need to be added to the list. The fields that need to copied include the Title, eBay title, product code (sku), description prices, brand, weight, website and category. We would like products copied into an Excel Spreadsheet so that we can import into Magento via Magmi. The description needs to be only copied across a text, we will then import into Magento. We don't need the images copied across or the descriptions formatted just in plain text. Some of the SKU codes will need to be re-mapped between the various sources, We will provide a list of the old codes to the new codes. Some of these re-mapped codes will already have a product that has been created and can be added a second (or third) website and description for importing into Magento via Magmi