J2Store customization -- 3

We're customizing J2Store as a "quote system" (so no shop functionality, no delivery options, no payment options). It's about new and returning customers can choose the amount of several products, check out and edit the cart and then send this cart as a quote to our customer. We offer the products in two quantities, in a big bag (in tons) AND (not or) in small bags (in amount of bags), so the customer must be able to use with two "quantity fields" and he must be able to add his remarks to each product. REQUEST A: "Hijack" the existing standard J2Store custom field as the quantitiy field # 1 (big bag) and then duplicate this field (with the same behaviour) for the quantity field #2 (small bag). Actually we have 3 fields, then (quantity1, quantity2, remarks) which we need to have in the product overview, the product details an - very important - in the cart overview (and of course in the mails to the customers and the shop owner). REQUEST B: All those fields need to be editable in the cart overview. The customer must be able to change the amount of both of the quantities and - of course - of his remarks( and save the changes with the standard "j2store update cart" button). REQUEST C: If the customers leaves the cart and adds more of an already chosen article over the product detail page, the article must be updated accordingly in the cart overview (not just added as a new line - meaning, in the cart overview there's always just one line for each chosen product).