Large school, everything takes more paper, goes through more people, and takes much longer. Many times at the campus level it is similar to the small school in that business managers, etc turn over less frequently than principals (at least in my experience). Problem is when it leaves your building, and the bigger the district is, the worse it is. Paperwork changes regularly (because the deputy assistant to the person in charge of making up new crap for you to do has to do something). Paper gets stuck on someone's desk that you later find out has been out for two weeks, and they are the only one qualified to approve your request for pencils because they have an MBA in pencil allocation. Policies and procedures change based on who answers the phone that day - and you pray for the day it is a janitor walking by the desk because that is the only time you will get a logical answer.
Bottom line, more time, follow up frequently until the process is complete, and do not expect flexibility. Best bet is if you have something like we had in the most disfunctional district I worked in. There was a long time secretary on campus that was our unofficial red tape jungle guide. She helped keep an eye on things and let us know when things went snafu, and when they did, she knew the people to call to get it straightened out. Befriend that person and treat them like the most important person in your life, because they are.