Hi,
1. Turn off the "force shipping regardless of weight" setting in your HikaShop configuration and make sure that you don't set any weight in your products.
2. If you just want to sell downloads, you can just add the files in the products under the Images & Files section of the product edition page.
If you want to sell subscriptions with access to files for only a certain period of time, that can be renewed, like on our website, you need to combine HikaShop with HikaSubscription:
www.hikashop.com/component/hikashop/product/cid-227.html
3. Yes. edit the price of the product and set its 'access level' to "registered" and make sure that the "display add to cart button for free products" setting is turned off in the HikaShop configuration.
That way, you'll be able to to remove the add to cart button for guests and still keep it for logged in users.
Instead of the price and the add to cart button, you'll get a "free" text that you can customize via a translation override to have whatever you want instead:
www.hikashop.com/download/languages.html#modify