Spent the last couple of sessions looking around the current code for a convenient place to start tweaking and adding, and decided on the various grids that are used as a visual aid. Currently there's the basic Grid (set at the current tile size), the Brush Grid (set to the current brush dimensions), and the Tile Grid (which overlays the Tile Panel).
At the monent these routines are reasonably well-integrated, but I'm torn between making my code streamline and modular (i.e. one routine that prints all 3 grids) as opposed to just slapping the code in where necessary and avoiding wasting cycles on function calls; ultimately it's cycles, not memory, that is likely to be my enemy, but I'm still not sure.
Once I was familiar with the code, I set about adding a transparency value for each of the grids; once it was in and working, the grids looked about a thousand times better (and the little highlighted pixels where the gridlines cross makes the grid appear reminiscent of graph paper). Finished off the session by adding a transparency value to the Brush plotting routine, and converted across the routine that allows the user to rename the current layer.
