I want to build an 8 foot 2x4 framed wall finished with stucco across the entry way to my home to create a courtyard. The sidewalk is natural stone over a 4 inch concrete slab. Do I need a footer? When digging on each side of the sidewalk I discovered PVC irrigation pipes a few inches below ground level. (Freezing is not an issue here.) Can I pour concrete over and around these PVC pipes.

I don't think you would have an issue with the wall loading, you probably have more load when people stand on the slab. 3 people at 200 # is probably more than the finished wall would weigh. As far as pouring concrete over PVC, make sure to place a larger piece of pipe over the sprinkler piping and the concrete will load on that, not the sprinkler piping.