Probably 있으세요 is the best choice among your examples and fits most cases. 있습니까 and 있어요 could be used a few cases, but when you say "higher position or rank at your office/school/etc".. it might not.
However, if it's YOU asking someone else that if you have something to prepare before the class (or whatever), definitely not "있으세요", especially with "시작하기 전에 준비해야 할 것들이 있으세요?" cause it sounds like you are asking someone if "He or She" has something to prepare.
And also you are missing subject in every sentence, so probably it's the best practice to add proper subject if it's YOU or I.
시작하기 전에 제가 준비해야 할 것들이 있어요?(있을까요? or 있습니까?)
or more specifically comes with objective as well.. then
제가 "수업을" 시작하기 전에 준비해야 할 것들이 있어요?(있을까요?