Regarding how to tell the quality of a blank. Keep in mind that quality is a subjective term that may be defined in many ways. What is "quality" for a downrigging rod won't be "quality" for a finesse rod. Think of quality in terms of what you want the rod to do and how its characteristics fit that. I'll talk general spin and cast blanks for the "normal" bass techniques and assume you are interested in the usual attributes like light weight, sensitivity, consistency from blank to blank, reliably meeting the description given for power, lure weights, and action, and reasonably durability and toughness. Although many times when the first two attributes are met they come with a sacrifice of the last two. High mod graphite rods can be fragile. I should add that the last attribute most of us consider is reasonable cost for the "quality" delivered.
To elaborate a little, a great finesse rod will not be a great cranking rod. A great cranking rod for little squarebills will not be a great rod for deep cranking. A great flippin rod will not be a great drop shot rod. No rod will perform at the great level if the lure weight is not matched fairly closely to its power.
Blanks are blanks. What are called spinning blanks can make great casting rods and vice versa.
First I would say that you get about what you pay for.
Stick with well-known, popular brands at least at first, until you get a feel for the different brands.
Keep in mind that after a certain price, like almost everything else, added dollars don't give as much of an improvement as they did lower in the price scale. I think there is a sweet spot that starts at about $60-70 for most regular blanks and ends at about $100 depending on the length and characteristics. Over that you're getting into the really high quality. Whether that makes sense to you depends on you. I have many rods made from the sweet spot range that are what I would call great rods for their intended uses.
What can make a great rod from a "sweet spot" blank is the quality of the workmanship and design (meaning all the components and their placement) that you provide.
What can make a mediochre rod from a great blank is the failure to provide the above.
Brands that provide a wide spectrum of blank "quality" are American Tackle, Rainshadow, Rodgeeks (where you get St Croix now, also), MHX and its derivatives from Mudhole.com, and I'm sure others will add their advice here. There are more, but the above are probably the most popular right now.
I would not build my first rod on an expensive blank. I did that and had to rebuild it later to fix it. Some do better on than I did on their first, but I think it wise to stick to the sweet spot for at least a couple rods. As I said, do it right and they can be great rods.
Buy one of the books on rodbuilding and search the web sites of the manufacturers for build instructions. Some are very good. (Mudhole.com, Getbitoutdoors.com, the Flex Coat youtube videos, and probably many more)
Read this forum and others (rodbuilding.org for one) regularly to get a good sense of what blanks other builders respect.