basically the old website, which as many many different types of products, is being changed into a "web mall" type website. The products, based on industry, will be broken down into about 10 different "categories" that will actually be leading to different domain names that still contain the name of the company.

REASON: the main selling product is very small and if the customer purchases over a certain amount of them, the shipping is free. if they purchase a large item on the same order the shipping would not calculate to be profitable. So, im thinking the larger items and the other items that do not sell as often will be on a completely separate domain with a separate checkout.

Question #1:

IS THERE A WAY TO AVOID THIS? I would like to have all of my items on the same domain, but I want to offer the FREE SHIPPING on ONE type of item only..when the customer buys a certain amount of that product.

Question #2:

Will this effect google's perception of my store? Since the main domain will have cross-links to the other "sub-domains", if you wanna call it that, im thinking this wont be negative SEO

Question #3:

Do you think the customer would be fed up? Confused? I know if they want to buy the small items to get the free shipping, they might also want a bigger item too.. but its not profitable to ship the large items for free.. in fact its the opposite

SO.. they would in theory, they would have to place a separate order on the other "sub domain" website for the large items and have to proceed with a separate shipping, order, checkout, all that..

Im looking for any suggestions and adivse if this is a good idea/bad idea..