Class - its a description of some data instance. Class itself can contain only static variables (and you cant create static in BP, afaik, only C++), all non-static variables exist only inside class instances, not in class itself.
Blueprints can only be debugged in PIE session. In order to properly debug an Editor Utility Widget, a workaround will be to click "Run Editor Utility Widget" first ( to start an instance of that class), then in the Blueprint Editor, attach it to this instance in Debug filter, and start any PIE(Preview in Editor) session.
There is no two dimensional array supported in Unreal blueprint.
UE4 reflection system does not support array in array (even in C++, regardless of fact that C++ allows to do so), so it’s impossible to make multi dimensional array. But there very simple workarounds which makes single dimension array to work like two dimensional array, by playing allocation numbers. If one dimension has static size, you can multiply that size in allocator by number of y positions, like this:
x+(x_size*y)
Of Corse you need to watch out to x not being higher or same then x_size or else it will read or set other y row. You can make functions to make it a lot cleaner and simpler
In Unreal Blueprint, you only can create an array, a map and a set of something for the data list. However, you cannot create an array of array. One way to get around with it is to use struct. You can create a struct A contains a array of struct B and create an array of struct A to achieve complex data struct in Blueprint.