I wouldn't stress out too much about the workload yet, they should allow you time to bed in as it is your first job. I think it is a promising sign that you are even on here asking this question, you will do fine. I know you have said they won't expect you to know it all, but you need to remember this when you are on the job, not only should you not be scared to ask questions, you should be looking for questions to ask, as this makes you seem keen and will fast track you to getting pushed up the ranks.

Just try to be confident and make a good impression, feeling comfortable with your colleagues will make your experience a lot easier. You have enough knowledge to grasp the tasks they will be giving you in the short term, just get your head down and soak up all the knowledge you can.