Word of advice: there should a guide in the game with hints how to achieve true end, which is required to access dlc/append story. Be sure to keep at least 2 saves and save often, especially before talking to main characters (those who can teach you more magic), because there are some choices that can make you "fail" their quest lines - you need good ending for all of them to achieve true end.
Thankfully, the guide should update each time you complete a side story for other characters so you know when you get proper ending.
There's more pregnancy in the DLC, after completing true end of base story if I remember correctly.
Different publishers, different version numbers. How many more years it will take before people will learn and stop asking the same questions every time?
I dunno. Maybe in some place where potatoes can be commonly found or bought - such as a market... He's not asking for some special potato after all so this quest is as simple as it seems.
btw. you have to complete this quest line to access true end so keep feeding them every day!