The cut outs look very sharp and risky to get something caught in.
That would be calling a “spade” a blade. . … those little pointy bits do look potentially painfully, especially when you tried to slide off.
You’ll need a “stretcher” between the arches … there is nothing to prevent the ends from spreading. The forward portion of the seat is unsupported; there is nothing to prevent it from bending down?
And you’re going to have to spend some time dealing with fasteners; you’ve shown what is essentially a two-dimensional form … what holds these three-dimensional pieces together? Bolts, welds, etc.