With regard to the cage and that hoop. You can use a net and or straps as well as the mandatory arm restraints in that area but this is what I see as the main issue. Lowering the top of the cage will give you much better aero,better aero means better conversion of fossil fuel to fastness and that's what we're here for.
When you lower the top of the cage you'll find the best way to get into it the car is to squat with your knees up and slide back as you straighten them. That's not possible with that bar there.
I'm not claustrophobic but wearing a -20 suit on a 100+ degree day in the cab of a tank will give you a fair idea of what it must be like, if you can indeed get in there at all.
I'm not sitting on the fence making idle comment here, I've been there, I've had to bite the bullet and make changes, I want to see you run this thing fast, soon.