What is the career progression to the senior NCO ranks in the Army?

Specifically do they only really come from combat arms or are they represented in all branches? What type of education both military and civilian is either required or common (i.e. is Master's degree prevalent in Senior NCO ranks even if it is not a listed requirement) What are their career lengths and typical promotion ranges in terms of years in service? Are senior NCOs typically enlisted for more than 20 years or are they retired from service at that point? Any other additional info is appreciated as well. Thank you.