Hey! Sorry for the late reply!
To answer that previous, unquoted question, UWorks is now finally on the Marketplace, but the price is acting weird. I wanted it to be 90EUR, the new portal forced to input USD so I selected 110USD (pretty much conversion rate) and for some reason, in my country it displays 118EUR.
For the new questions here: UE games use USaveGame objects to store data. The entire functionality is pretty much exposed to BP as well and from my experience they work well pretty well. In your case, they may not be the ideal solution, as they are essentially locally saved/read files with custom data and that’s all they are.
Steam can store your data, yes, with the above-mentioned interfaces. However, to avoid overflowing their sample 480 AppID, some stuff requires your own unique AppID. The process of storing data is described rather well in these links:
https://partner.steamgames.com/doc/features/inventory
https://partner.steamgames.com/doc/features/achievements
https://partner.steamgames.com/doc/features/achievements/ach_guide
https://partner.steamgames.com/doc/features/achievements/stats_guide
Hope that helps!