You just need to create animations for the directions you want. Delete the animations for north & south & it will automatically use the closest direction available based on the direction the character is walking. I think for side scrolling you need all directions except north & south, no?
It might be an idea to create another outfit with north & south directions in case you need them for something - like entering a door maybe.
As for making sure player walks only on horizontal path you need to create close together way borders to severely limit the amount of space the character can move.
Another member on here: "SDMono" has created at least 2 side scrolling based point & click games using Visionaire Studio. This
is the one he's currently working on.