Sorry for the late response, just saw your posts.
This FAQ might help: http://www.theflyfishingforum.com/fo...uld-i-get.html
It's a general discussion of different types of hackle and gives some specific recommendations based on type of fly and budget/bang for the buck.
But to answer your question yes, you'll want to get hackle that is sized properly for the hook sizes you'll be using. For dry flies, the barb length should be about 1 1/2 times the distance of the hook gap. Depending on the sizes you want to tie and your budget, there are a number of ways to go.
For a full range of common dry fly sizes, say size 18 or 20 on the small side up to feathers for tying size 8 or 10 dries you would probably be best off buying a cape or 1/2 cape. Something like a Pro Grade Whiting Hebert Miner Cape runs around $30 for a whole cape in a single color. The Whiting Introductory Combo pack consisting of 4 colors ( grizzly, dun, brown and one additional color) is another good deal for $60, especially if you can find one that has the 4th color of the pack in ginger since that will cover a wide variety of fly patterns. A 1/2 cape will have the same sizes as a full cape, just half as many feathers.
A saddle will have a more limited range of sizes, which is fine if you can find a saddle with feathers in the size range you want. Unfortunately decent dry fly saddles are in short supply because of the fashion craze for hair extensions.
Another option is to buy pre-sized hackle, like a Whiting 100 pack. These are packages of 12 or so loose saddle feathers in a single size and color
for $18-20. Because the feathers are each long enough to tie many flies, you should be able to get around 100 flies out of a single pack. Although less expensive unless you only plan on tying a single size, you'd be better off with a whole $30 cape (or that color 1/2 cape in the introductory pack which would work out to $15). On a cape, the feathers with the shortest barbs are attached to the skin closest to the top (near the v notch where the head was cut off). Barbs get longer as you move to feathers attached further down on the cape.
To size feathers from a cape of saddle to given hook, bend the stem around the shank to see where the barbs end in relation to the point. It's a bit awkward to do with the feather still attached to the cape or saddle, but it can be done with the hook in the vise. A Griffin Hook and Hackle Gauge (about $5 or 6) is also helpful. It has a pin and a series of concentric circles. You bend the stem of a feather around the pin and see which ring the ends of the barbs reach to get the size of the feather. Here's a pic of one surrounded by different types of hackle pliers:
I hope this helps a bit-- feel free to ask questions about tying in the fly tying forum-- you'll probably get more responses. Unfortunately local fly shops can be hard to find in many areas, and buying materials over the internet can be really confusing, especially if you're just starting out and on your own without the help of someone that's been tying awhile to help pick out the right stuff.