There is no limit to the number of carts that you can have in your draft cart folder.
A Hosted Catalog will make sure that the appropriate pricing is accounted for. However, for Punch-outs, you will need to check the supplier’s punch-out site for pricing and availability.
Yes, you can copy an entire cart for reproduction.
From the "available actions" drop down menu on the original requisition, you will see the option of "copy to a new cart". This will transfer your cart's information without having to manually type everything over and over again!