Depends on what you want to tie. When I began tying as an adult (I won't go into my teenage tying adventures
), I wanted to tie every fly known to man. My extensive collection of materials reflects that, and I'm always being surprised to find something that I bought and never used. The dry flies I tie 99% of the time are blue wing olives, Adams, light cahills, and various elk hair caddis. Nymphs are GRHE, PTN's, Zebra midges, and Green Weenies. Wooly Buggers and Clousers round out the rest of the flies I use 99% of the time, and I can catch fish reliably with these. It's probably best to focus on tying a limited number of patterns at first, and mastering your tying skills: thread control, material placement, proportions, symmetry, etc.
Buying a neck will give you a wide range of feather sizes, but that's not much use if you intend to tie 100 Adams in sizes 16 and 18. The larger feathers will give you material for tails, but there are better tailing choices: less expensiverooster necks can be purchased for $15-$20, and are fine for tailing. I use microfibbets for tails on BWO's. The only tailing materials used on Elk Hair Caddis are used when tying X Caddis (very effective fly!), and that's antron.
I like Whiting hackle becuase it has thin stems. You can find less expensive hackle, but it's important to look at the stem thickness. Thick stems are awful to work with, and thin stems are a joy. It's just that simple.
The cheaper necks I mentioned above can have thick stems, as I use them for tailing materials, and the stem is irrelevant.
I do have Whiting 100 packs, and hardly ever use them. It's been my experience that the stated size varies from pack to pack, and sometimes the stems are thicker than others. Honestly, the best way to buy hackle is in person. I bought some Whiting 1/4 saddles from Cabelas, and while the dun and ginger were dandy, the grizzly hackles were terrible: the hackle on one side of the stem was twice the length as the hackle on the other side! I bought it online, and didn't feel like returning it ($25 Bronze grade). I have Silver grade Whiting that is spectacular, but one brown saddle has thick stems in the size 16 hackles (all of the other sizes on that saddle have thin stems
).
So....What do you want to tie, and is there a good shop nearby?