The interchangeable sets seem like a nice idea. Especially when you start to use circulars for everything instead of straight needles. I recommend that you not buy any until you need them for a project. You inevitably buy a size that seems common and it wont be what you need for your next project you just have to do. WE all have tools and yarn we thought we would need and ended up not using
. I dont feel so bad about spending money when I wait and buy exactly what I need when I need it.
I learned this from watching my mother overbuy and tell me she regrets not only buying what she needed and also keeping tally of what she had before she bought again. I bought her a circular needle organizer and she has 5 size #8...all the same length. She cringed at all the repeats she has bought over the years.
Enjoy your new addiction...I know I am!