circular needles

[allynealy]

I need help, please
I bought a denise set and really like it. I need some smaller needles now. I was thinking knit picks harmonies.
So, my question, what sizes are most useful? I thought that I would get size 0,1,2,3 in fixed circular 47" and that would allow me to do magic loop. Do I need all of those sizes, or can you substitute different sizes without too much difference?
Also, what calls for 16" circulars in those sizes? Do I need to get more cable lengths?
I am new to knitting and really like magic loop. I tried dpns and don't really like them. I am going to stick with the circulars.
I am planning to do socks, hats, baby sweaters, gloves, diaper covers, babylegs, and maybe one day a sweater for myself.
TIA,
Allyson