A Few Functionality Questions

Hello everyone!

I have a few questions and would love some feedback/fixes! (I’m using UE 4.20.3, originally I had imagined this project as 2D, however if AI presents an issue, I will do 3D accordingly.)

To begin with, when I drag my mouse over the mesh, it is supposed to highlight once every 200x200 squares, as you can see in the Gyazo GIF, 2 things happen. 1. It doesn’t follow the mouse correctly, and 2. It stays highlighted even though the mouse has moved to the next 200x200 square.

Secondly, I was curious as to how some of you would implement puzzle piece selection based off of a menu widget (buttons). Click the button -> a ‘ghost piece’ should appear to give a preview of what you’re going to place -> when you click on the ‘grid’ to place, the ghost piece disappears and the real mesh appears.

Thirdly, AI. What would be the most efficient way to make the character seen at the bottom of the screen run to the center of the block, along these newly placed paths?