i'm quite new to this too! i had the same readings as you (a series of zeros!) despite me having fish in there. i assumed that the zeros were good and thought i must be cycled. i was then to learn that without nitrate you havent cycled. also bear in mind when you do get nitrate, keep it below 20ppm. if you havent read this already, this article is definitely worth a read:
http://www.fishlore.com/Forum/aquari...d-first.0.html
i then made the mistake of putting more and more fish in, which has now tipped my ammonia over, and now i'm cycling with loads of fish in there!
someone else i'm sure will give you advice as to why you have no nitrate when you have so many fish in there (i read your welcome post which listed them all! - i hope i have the right person and havent got you mixed up with someone else?!

). are you using the test strips as they are notoriously inaccurate. if using solutions are you shaking the solution thoroughly as directed before use as the solution can seperate and give false low readings. plants will use some nitrate too, so if you have those thats worth bearing in mind.
you say your stats have been fluctuating? did you have ammonia earlier then and nitrite and nitrate?
i've never vac'd gravel yet, so i cant answer that. as i'm stil cycling and the good bacteria are in there i darent touch it and remove any! i need every good bug in there i can get!!!
wish you good luck, and sorry i couldnt be more help!!
Tan