Progress is still going smoothly. I've finished the tile sets for the desert and winter themes, so the only outstanding tile set set is for the volcano levels. The sooner I solidify all this content, the sooner I can begin to tweak the difficulty curve.
For the walkable path, I use a total of six square sprites for each theme (horizontal, vertical, four corners). At first I attempted just to use one corner piece, but that easily causes seams and result in inconsistent highlights and shadows anyways. For a seamless horizontal piece, just create a square movieclip and then then tile it. Select one in the center, and then begin working from that because you can preview it as a pattern where the surrounding pieces are grayed out.
The props (e.g. skulls, snowmen) can be deleted during the game at the cost of gold. I actually create and place these as movieclips in Flash where each property name is the same as the name of its corresponding member of the sprite sheet. The level is exported as a .swc so I can I can use FlashDevelop to take all these levels and output debug text describing the location and type of each prop, formatted as Lua code so it can all be copied and pasted in one go. It may be a strange way of doing things, but it's very easy and rids the need to introduce a level editor because Flash is the level editor.