I think it's up to your own level of organization and how much sleep you need and how you let anxiety affect you as to what is do-able for you. For me, first semester would have SUCKED even more if I'd loaded micro into it. The nursing school culture is something you don't understand until you are dropped into the middle of it with the crowd of other frenzied student nurses around you making it feel that much worse.
If you can safely take the micro over the summer, you'll have that much less to worry about later.
On the other hand, I'm doing micro now (in my second semester) and since I'm used to the course load in my nursing program and used to the craziness all around me, I'm probably going to be able to pull it off all right. You know, probably. It is a LOT to do while you are also expected to produce quite a lot from your program courses, but again, that's something you'd know better about yourself than we do. How organized can you be and how much stress can you handle and for how long can you expect to handle it? Personally, I am counting the weeks. I can do anything for one semester. Six weeks down and ten to go.