rear ended in severe accident trying 2 handle without lawyer

I was rear ended in a severe multiple car accident where myself as well as other vehicles were stopped in traffic on a highway and the at fault driver plowed into the stopped vehicles at over 70mph according to the police.

My car was totaled and i had to go to the emergency room in the ambulance. Luckily nothing was broken but since my neck back and right hand have been messed up since. The accident was over a year ago ive been seeking chiropractic care for a year and now im told that I ve reached "maximum medical improvement" and have a percentage permanent injury. Not sure what that means but Im going to see about continuing treatment at another doctor.

The at fault driver has a $1,000,000 injury policy and himself is very wealthy. I would like to know what to ask for in my initial demand letter to the lawyer representing his insurance. The accident has really affected my life for the past year and even now just sitting cause me back pain and i have nerve damage in my hand. My neck is almost always stiff and painful and i get migrane headaches. I never had any issues like any of this before the car accident.

Any advice is welcome as I have not hired a lawyer yet first want to see what i can do on my own to avoid paying out 33%