A pitch page is one which your customers first see (its where you talk about your product, give some 3D cover photos, maybe a video)
The thank you page is the page they go to after their order, typically it will show a thank you message and give info on the payment and bill they just completed. The download link to the product is often on thank you pages, although this is sometimes considered insecure.
For eBooks use Word 2007 with the PDF export version , or XPS which gives much smaller files and only uses an internet browser to open (by much smaller i mean 3 megabytes for XPS and 30 for PDF ! )
As for Ebook covers, DIY or go to Fiverr, some people on there are excellent and can deliver the flat versions of the files aswell!
Hope this helped you out