1). Split Polygon tool has a snapping tolerance option, you can choose how powerful to make the snap, and where along the line to snap. It defaults to 50% along an edge, if you increase the tolerance then it will be more likely to jump to exactly 50% if you're near the middle of the edge. Unfortunately without custom…
A note on negative scaling: make sure to freeze your transforms afterward, and then bring up the attributes on the mesh and uncheck the 'opposite' flag under the render tab. You'll have to uncheck 'double-sided' first before it will let you uncheck 'opposite', then re-check 'double-sided'. I put together a short script a…