I have a Nova, a very old one with a 24" barrel currently and it's a very good gun. The trigger was terrible and it was very stiff overall when it was new. I dry fired it a lot and then took it to the range, any range, any time I was shooting and shot it as much as possible. I also loaned it to anyone who wanted to shoot and now it's as slick and smooth as any pump gun that I own.
I don't shoot Nitros so can't be of any help to you there. I do shoot a lot of Hevi-13 shells and they pattern exceptionally well. There are several chokes that work well, most in the .640 to .655 range, depending upon the "internals".
Good luck with your Nova.
Thanks,
Clark