Create an array that holds a grid of vectors that matches your block spacing. Then, use that array with a ForEachLoop outputting the array element to a SpawnActor or AddInstance node.
Easiest way to create the array would be to use 2 ForLoops lined up, 1 for X, and 1 for Y that use their index to increment your vector by however many units prior to adding the vector to your array.
Here is my vector array generator, but it is for hexes:
First of all if you want a large amount of blocks just use his plug-in.
It’s not actually a few thousand actors because that would be horrible performance wise (worse than minecraft itself and that was pretty horrible in the beginning and is still only meh).
It’s only rendering the outlines and is actually pretty ■■■■ complex.
To your question directly. Just use the normal coordinates and normalize them to your grid. With that I mean if you spawn something or break it check for the collision point and find the closest point in the grid. Your grid is for example 200x200 units large. So if you want to build a block just get the nearest point which is on that grid.