Really all that you have to take off the mast before unstepping it is the sails, the boom and running rigging that's attached to the boom. Some people remove the shrouds and stays (cables) from the mast and coil them, others leave them attached to the mast at the top and secure them with a line. It's up to you but I find that leaving them on the mast is easiest. The turnbuckles will not be seized, no worries.
Taking pictures will help you put the puzzle back together after it's taken apart. Watch the yard hands as they unstep the mast, ask questions but try to stay out of their way, you're paying by the hour.
Removing the spreaders is no big deal, one bolt on each side usually.
When you're stepping the mast, you need 2 or 3 friends to help you. Friends that own sailboats and have done it before. I won't try to explain the procedure here. It's simple if you get it set up correctly before you start, it can be a nightmare if you don't.