Or do I need to rotate with other crops?
It's like a lot of things, it left its pests behind when it was brought here. So it's not going to do any harm. Only thing is, if you always grow it in the same place, it'll be taking out the same nurietns, from the same level in the soil, year after year. So, no need to be neurotic about rotating it, but as you'll probably have other crops which do need rotation, it's probably best overall to include it in the system.
What group does it belong to for rotation?
It's a grass.
Needs a lot of nitrogen, I sowed a nittrogen fixing crop between mine this year, they seemed to like it.
Well, there are so many crops you have to rotate like brassicas (club root) and onions (white rot), sweetcorn is a good disease-neutral crop to follow these.
But it is VERY hungry, very depleting on the soil so you need to add loads of good stuff before and after.
So I've got it in as part of the plot rotation but there is no reason from a disease perspective why you couldn't grow just sweetcorn every year AFAIK.