Sub-frame connectors... Please build them correctly!

I can see your point on the bolt in connectors in the bottom 2 pictures, but weld in 2X3 connectors that go under the floor is a good option too.
Your set up is ideal, but include a properly fitted and installed 10 point cage, now we're talking.
It all depends on what you want, need, and expect out of the car......
Skin the car and put a full tube chassis under it is ideal if you want to really split hairs.