I see a lot of loose "projects", but try to fit (as much as possible) into one single project. Make a line following robot, that balances, has WiFi communication and a display.
Putting all the different parts together may create whole new problems/difficulties.
Stop using Arduino?
Find another IDE, so it's easier to manage a lot more code.
Learn how to set up a toolchain/compiler.
Try programming an ATMega328P without Arduino.
Why? Because it'll learn you how to other devices work, if you're comfortable programming an AVR without Arduino, it's just a little step to using PIC microcontrollers.
Design yourself a PCB specific for the project you want to do.
Work on "Professional skills"
Try to make some actual designs, requirement analyses and make a report on the project. This way you can practice for school/future jobs' professional skills.
So what project should you do?
Something you would really like to do.
It's as simple as that.
Something of which you think is going to be a challenge (but not too challenging).