Is there a way of 'painting' or 'filling' tiles? I'm filling in a large area of background tiles, and it's very laborious clicking and dragging every single one. Is there a fast way?
Yes, you can quick-fill areas in most locations, and at most ranks. To do so, find an empty space and and place tiles in the following order:
1 2 4 3
2 1 3 4
That is, only the 4 edges, in clockwise or counter-clockwise order starting at the top. This will work with many block types (like solid, back, liquid). A video of this in action can be seen here.