set images to categories and link them to other pages

I would like to put category images in a grid view on my main website page, I want each image to link to a category page in my store, there I would like to put all it's subcategories' images that will link to the category's products lists.
basically, I am asking to know how to set a featured image to a category, attache it to a page in a grid view like I (present products with marketpress) and link the images to different pages.

also I would like to know if there's a way to change the shopping cart to a quotation form, therefor change the way the product is shown (remove price field) and instead of add to cart button, ask a quotation button.

thank you
looking forward for your reply
Itay Farjun (temp address)