Hello Creative1
About programming.
It's up to you, what language you will choose. If you choose C++, It will be still easy to program because of very clean and simple API.
Example:
TEntity = myobject = CreateSphere();
PositionEntity(myobject, Vec3( 0, 10, 0));
RotateEntity(myobject, Vec3(0, 0, 90);
So, you can see, commands are intuitive, simple
About GUI:
You have to draw them self and put images on screen for example or you can draw them by opengl/engine functions like Line, Rectangle ...
TTexture hud = LoadImage(" path ...");
DrawImage( hud, x, y );
so, pasting images is pretty easy too
Drag and Drop ?
Yes, you can use Editor .. you can drag models and drop them on your terrain, anywhere and you can script them using LUA script
Of course, game development is about programming, so you have to know basic of C at least and you are fine.
You can look here for documentation: http://www.leadwerks.com/wiki/index.php?title=Main_Page