I share your 'never made a chair before' inexperience Mike; so my comments have to be taken in that context.
1. That looks like a flat (horizontal) seat - I'd read a bit to see if the recommendation is for a slightly angled back seat; 2-3 deg is what I recall reading - bit I am not certain about that. With the sculpting in the seat, it may even 'lean' forward, which I believe is disconcerting to sit on.
2. As you know, leg joinery choices are critical - those front legs, connected at only one spot, are especially vulnerable/critical. While it takes away from the simplicity of the design, and makes fabrication more difficult, lower chair rungs dramatically improve the strength of the system.
I too plan to make chairs someday! I will follow your adventure here.