1. Sitecore XC uses new Databases Global and SharedEnvironments. Within these Databases there are a few tables named XXXLists and XXXEntites. Within these Entities Tables Sitecore XC stores all the entities like sellable items, price cards, promotions, orders etc.
2. That's already done OOTB via CommerceConnect. Commerce Connect is a full integration between Sitecore XP and Sitecore XC. This contains some API functionality, Analytics, but also Product handling in Sitecore XP. As you can see in the Screenshot, Catalogs, Categories, Products and Variants are shown as so called virtual Items. In the end these items are items and every interaction at this place triggers a corresponding functionality in Sitecore XC to update the changes there.
Note: From Sitecore XC (9.0) on the stong recommendation is to not use Content Editor for Commerce item / information handling. This can also be seen in the fact, that the commerce items are OOTB protected. At least content editors should only use Business Tools for Sitecore XC related content handling
3. Publishing of Sitecore product "items" or better entites is not done in Sitecore XP and not done via standard publishing mechanism of Sitecore XP. Sitecore XC has its own publishing mechanism to publish sellable items. Such publich mechanism as it is implemented now has OOTB no future publishing possibility.
So in the to use price cards for furture pricing in general makes sense for commerce sellable items. In addition to that setting, price cards enables you to set currency based pricing, tag based pricing and tiered based pricing for now and the future with setting snapshots, which is for pricing far more powerful than, the item publishing mechanism