I am an experienced Unit Coordinator in the sciences and, although I have panicked a number of times during the past 13 years, I have learnt much that I can share with incoming academics. My general advice would be to expect that things will go wrong and not to panic; to reflect upon and analyse components of the role and improve upon them and, if taking over a unit developed by someone else, to only make small changes. Ask any previous unit coordinator to share their student evaluations and use the results to improve the unit that is now yours. Nothing is set in concrete and, while your changes may not be perfect, students do survive and they move on. All Unit Coordinators have their own way of handling things, as will you.
Other suggestions I would make include preparing the unit manual as early as possible while considering university breaks and public holidays, as a missed laboratory session on a Monday or Friday (holiday) by one or two groups will have huge implications. If employing sessional lecturers and tutors, plan well ahead to enable them to plan also. Locate templates for them and ensure they are clear about the assessment tasks because these drive student learning. Also consider the lab technicians who will need, in some cases, weeks in advance to purchase chemicals, etc and prepare for multiple classes. In addition, notify the timetabling and rooming people of your schedule well in advance so times and venues can be booked to suit you.
Realise that while you may be prepared to work until 10:00 pm the night before a class, there is no reason why anyone else should do so. Much angst is generated from the time and effort exerted to improve a unit and innovate. However, accept that this will rarely be well recognised or acknowledged or rewarded by the university. I do the work because it brings me satisfaction and I believe my efforts will improve my students’ learning. Incoming academics will need to identify their own drivers. Finally, while I have not found the sciences particularly collegial, I would try to build a network of people you trust. Having good interpersonal relationships is the key to enjoying the workplace.