Don't worry about ejection pattern, until this thing is broken in. That isn't the end-all/be-all anyway. I don't care where my brass goes, as long as it gets out of the gun, and the gun functions. I don't set any rifle up, ever, based on any ejection pattern.
Next, always start an adjustable gas block wide open. All the way. You save ammo that way, if you want to hear my version of the story. Always, Wide Fukkin Open to start.
You need to spec these out, and find out what the details on the recoil system are. And post the results. You listed the weight of the buffer at 5.5oz, and that's a good weight. What's the length of the buffer? What's the internal depth of the receiver extension? I'd shiitcan the spring, just because it's an unknown. Unless you can give a relaxed length, wire diameter, and coil count, it's an unknown. Beyond that, we'll never know if it's chrome silicon, or what the material is that it's made of. Those details are super important.
After the recoil system is solved, we'll move to the gas system - unless you want to get to that now. Pull the gas block, and measure the gas port diameter with numbers drill bits, use the shank of the bit to measure.