So:
OnEventBeginPlay - Set Idle = Yes
On Key Press W,A,S,D - Set Walking = Yes, Set Idle = No
- On Key Release - Set Idle = Yes
On Key Press Shift - Set Running = Yes
- On Key Release - Set Running = No
You can make it so that Walking sets both Speed and Stamina use. Running merely multiplies it, so if not walking but shift is held down, you don’t move and there is no stamina use.
If you have different run states or multiple ways of setting speed you can get more complicated with the bool statements and it should be able to cover every case.
In case you didn’t know, you can run multiple executions from branches into the input of another branch. So true on Branch 1 goes to Branch 2, and False on Branch 3 also goes to Branch 2. (Edit: Though now I realize this is an OR node? Wish I had made that connection days ago… 
Boolean Operations - C++ Tutorials FTW)
If none of this helps I am sorry, I may not understand the holdup at this point.