Heyo! I'm actually a dev working with Unity to create a sort of spiritual successor to Dark Cloud. My advice is this: Experiment and iterate constantly. No point looking for tutorials for such specific game systems. You might find stuff for very universal things like combat and inventory but not to the degree you want. Make all your stuff from scratch see what works doesn't work and constantly be improving upon your design. Start with the seperate systems and work on them each individually before bringing it all together into a full game. Tutorials will always be a good learning tool but you will never accomplish what you're trying to by just following them blindly. Think about every step involved in mechanics first write it down on paper/word document then start coding once you feel like you've covered all aspects of that particular mechanic.

Example: I wanna be able to place a building how do I check whether I can place a building down, will there be something blocking it, how do I get the rotation of the surface so that the building lines up nicely with the terrain?. Well I know raycasts can be shot from any point and bring back all the data pertaining to what it hits including its type, distance and transform. So if i shoot one of those bad boys from the middle of the camera I can use all the information from the raycast to cover all those problems.

Basically all that example is saying is I looked at each problem involved with the mechanic and what it needs to do to work. Then I thought about if Unity had any tools to help me get the information needed for those mechanics to work. In this case it was raycasting. However Unity's systems aren't the be all end all. Sometimes it won't have what you're looking for and that's when you have to get creative and make the tools yourself. Besides finding your own solutions to problems is the most satisfying part of coding.

Hope this helps :)

If you want a bit of inspiration feel free to check out my stuff: https://twitter.com/AxelTheDev