Welcome to the boards and the quilting hobby. Some of us just take to this idea of putting pieces of fabric together!
You will find I rarely have a short answer to anything, and that's partly because there are many ways to do things or to approach design considerations or challenges. My short answer for you is "probably a couple of layer cakes and maybe some coordinating yardage".
And here's the tl;dr (too long; didn't read) version:
So the first thing to start thinking about is what is the size of project you want to do. Personally, my design mind is set on queen sized projects. You might be set on another size.
The next thing to consider is the type of project you want to do. The more seams it has, the more yardage it uses. A small triangle can have as much fabric behind it in the seams as you see. A lot of the more modern quilts are based on fairly large blocks/grids and aren't as "fabric intensive" as others. Do a google/search on 5-yard quilts for example.
Thirdly, is how you wish to sew. I spent a couple of decades being very precise in both my cutting and stitching. Now I rely on my 1/4" seam capabilities and do most of my work cutting/sewing large and trimming down for my precision. I used to sniff at the technique of making small HST by sewing down the middle of a square and trimming off the portion you don't use as being fabric wasteful. Now, well -- if it is so much being trimmed off that it bothers me I'll make a bonus unit from it and otherwise it is faster and more precise for me even with the extra trimming.
So with a queen sized project for rough planning purposes I start out with 10-12 yards for a queen sized project. Half of that is 6 yards. If I truly love a fabric this is the amount I buy but that is rare. I have another friend and she starts her buying at 6 yards to the rest of the bolt if she loves something. Mostly I buy cuts that are between .5-3 yards as being the "most usable size when I don't know what I'm doing yet".
I like the layer cake size, way back around Y2K I did a lot of fabric swapping, that was largely before precuts but we determined that 10" squares were a good size both for swapping and ease of use. In the last 20 years I've used a lot of 10" squares in many ways... (16) 10" squares is roughly 1 yard of fabric to put that in the equation.