Ray, your going to have to decide which type and brand of blades you want to use, I've tried a few different brands and settled on Flying Dutchman brand. Others have different brands they like better, but that's them, not me. You have to do the same thing, pick a brand and stick with it. Otherwise your going to have so many different types and brands of blades, you won't know what type or brand your using. No matter what brand you choose to use, they all have different types of blades for different types of material. So no matter what brand, you can find a blade in that brand to use. Once I settled on the brand I was most pleased with, I gave away most of the blades I owned of other brands. I've never regretted my decision, FD blades do everything I expect and want them to do. For saving blades, if they're worth saving they go back into the container they came out of. I don't save many blades, they are cheap enough that I don't worry about saving them. I used to save used blades, I stopped doing that because I never used them.
As for the dullness of a blade, to me, that a feel type of thing. You should be able to feel when your blade is starting to not cut as well as it did when you first starting the cut. Plus, it will take more force to feed the blade into the wood, or the wood into the blade however you want to look at it. Plus, if the blade is real dull, you'll be able to tell from the amount of smoke coming off of your project.
Len