hello Leon, I'm sorry you couldn't reach anyone on Steam. to quickly answer your questions:
1) you can choose to save game progress for every completed course, castle or world. there's also a command which allows you to save anytime
2) there is a shopping system in the engine. as for inventory, it's not a built-in feature and it is convoluted to implement, but it's possible. it would require the use of variables.
3) yes
4) no, legdes are not grabbable
5) you can modify player psychics (speed, jump height, wall traction etc.), as well as some values like health, ammo or air (time spent underwater). other values (hunger, thirst) are not bulit in. similarly, you could implement them as variables but it would take some time
6) yes. there is a setting that allows you just that
7) NPC settings allow up to 10 different messages. you could also convey dialogue with different types of in-game text. missions/quests are possible, I'm implementing them in my game.
8 ) yes and yes. mouse inputs can be recorded in Character's Command Prompt settings
9) aside from area-bound particles (rain, snow and thunder), every item special effect can be used.
10) no. lenses as well as some other assets will be removed from your executable exports. the engine will let you know which, with a small circled exclamation mark. lenses don't really have a replacement (sorry).
11) we have a Discord server
https://discord.gg/JGq2mv5My answers were only surface level, let me know if something's not clear. I'm happy to help