This is a very loaded question, and I don't think there is a clear answer like you hope for. Asking what to learn for ignition is kind of like asking what programing language you should use. It completely depends on what you are doing.
For example, I have touched vision once or twice pretty much exclusively using perspective, but some companies only use vision and no perspective. Some employers might have all the modules and others may have one or two.
I can't think of any projects that would help gain you any more experience than just poking around.
If you are trying to learn I would highly suggest just trying to read any threads about tips or anything like that. Here are some that I know of
Useful CSS Stuff - Ignition - Inductive Automation Forum
Ignition Best Practices - Ignition - Inductive Automation Forum
Some topics may have some overlap but there's some good pieces of information in those.
Also, don't underestimate the user manual and forums most questions you will have, have already been answered. If not, there are lots of active users on the forums that are happy to help.