choice of chickens

First of all hi to everyone I am new to the allotment/chicken forum.  I am very interested in keeping chickens in my garden- I have chosen the house been on an introduction to chickens course and have had loads of advice from a neighbour who has chickens (7)  my question is how many do you have to start and do you have hybrid or pure breed?  The house is for up to six chickens and I had been thinking that 3 chickens would be okay but now I have been told that 3 is'nt a good number!! any advice would be appreciated

I have Black Rocks and can recommend them for a first timer which I was when I got mine.     I also like bantam breeds (I have Wyandotte, Welsummer and some hybrid bantams) which are less messy but not necessarily quieter.