I don’t know how long you’ve been knitting, but I have just a small word of warning. (Maybe it will be helpful to someone else, if it doesn’t apply to you).
When I started knitting, it seemed wise to build up a little stash so I didn’t have t run to the store every time I wanted to knit something, and because everyone seemed to have stash.
So I started buying a couple of skeins of this or that when I went to Michael’s or JoAnn (two craft stores here). I had built up quite a bit (by my standards!) and was gradually learning to knit better, and learning new techniques and all. Suddenly, I reached a point where I needed more of a certain color than I’d bought, and it wasn’t available. Or I wanted to knit a certain project, but it called for a yarn I didn’t have. So, I started looking for projects for the yarn I did have…and often couldn’t find anything appropriate.
Ultimately, I was left with a fairly hefty stash of stuff I really didn’t like any more, or a bunch of different colors, but not enough of any one color or matching colors to do a larger project. (By choosing the same line and weight, you might eliminate much of that problem!).
While I was building for the long term, in the end, I needed change long before I ran out of “stash.”
If you know what you knit, and don’t anticipate too much change, no problem stocking up on a lot of very similar yarn. But if you’re not sure what you’ll be doing in 5 years, you might want to consider quantities and variety as you go.