Tim is right, model only have than mirror it,
For me, I would just use extuded splines for everything except the seat, for the back just model 3 different splines, and remember when modeling the seat, make the seat the same width and the back, so it blends in nicely. Same with the handlebars and top part (that connects to the handle bars) use a spline, and just scale it accordingly.
At the bottom of the chair legs, I see little extrusions, but can't exacty tell what they are, a more detailed and better quality image would be better. For the seat extude a spline, convert it to an editable polygon, maybe use the cut and tesselate and some other tools, to get the polygons you need to model the lip that goes up at the end of the seat.
Hope this Helps