My first (and still only job) has been as a float pool nurse at a 260+ bed facility and I LOVE IT!! I get SO board with repetition and this has really been the only thing that keeps me interested and on my toes! You definatly do need to feel confident about yourself, but I also got 3-7 days on each unit I would float to as orientation.
Since I started I have been expected to float to all the units you listed plus psych, urology, pediatrics, and mother/baby. But I really love the variety I get from it, learning ALL specialties! Plus I get to know ALL the staff from ALL over the hospital, It's great! (especially when I have an inpt family memeber cause no matter what floor they are on, I know the nurse caring for them!)
I was once told that if you aren't nervous that you don't care enough! So have fun, learn a lot, and just don't forget to ask for help when you need it because everyone does at sometime!