Very nice job on this one!
Thanks for sharing! Good to see you keep on the safety side and do the welds properly with pre-heating. You may already have this in mind, but I will tell it just in case. I would suggest a few extra reinforcements here and there.
1. One may be an additional member added to the upper rear control arm (pictured below). That will unload a good portion of forces from the lower control arm joints (bushings?) next to the wheel hub.
http://i.imgur.com/24LVAnF.jpg2. Then, you may add one vertical tube to connect the horizontal ones on the chassis where the first coil-over is located. That will increase the strength significantly as the massive bottom tube will help support the upper ones when pressure forces are applied to the coil-overs during acceleration or high-speed cornering.
http://i.imgur.com/ArEhOhc.jpg3. Also, one removable cross-section tube (or even better, a X-brace) to connect both sides of the upper mounting points will help a lot.
http://i.imgur.com/Ksls4Ch.jpg