The answer depends on where you live, and what type you have brought.
In many countries that import chickpeas they heat treat them to kill seed-borne diseases and insects. The heat treatment process makes them more difficult to cook, and soaking times double or triple.
Beans from exporters with phytosanitary certificates can be imported without heat treatment; these are the ones you want to get.
I don't think you can tell which is which by looking at them. At the moment we have some particularly dark, dry, and dead looking beans that soak up beautifully in 8 hours!
Soak non-heat treated beans for 8 to 12 hours, heat treated beans for 24 to 36 hours. Some overly heat treated beans will never fully revive, and you are best to return these to the shop as "faulty".
Soak and cook without salt, unless you are going to mash them. They fall apart more readily if salted.
If you are not mashing them, the secret to great chickpea taste is after soaking and cooking in water, is to lightly fry them with a little olive oil until dark spot appear, keep them or the pan moving so none burn. Then add the sauce, or add them to whatever dish you are preparing.
Roasted, salted dry chickpeas are a snack food.
I would not expect for you to be able to make humus out of them; for one thing, they would have way too much salt, and the texture would be wrong. It might be possible with a lot of experimentation, but you'd need to go through several failed batches before you got one which worked. Personally, I'd just go back to the store.
Best Answer
Boy is THAT ever controversial. It seems that everybody has a theory as to why some beans float while most do not. The most common answer is that the "floaters" are older, and less hydrated to begin with. Some people insist that some beans float because worms have gotten into them. Hogwash, ignore those comments. The bottom line is that "floaters" are perfectly safe, and there is nothing "icky" about them, although they may take longer to fully cook. So, it becomes a matter of personal choice. If it's important to you that all of your chickpeas cook to exactly the same degree of tenderness, throw them out. If you don't mind a slightly (and I do mean slightly) chewier bean here and there, keep them. Personally, I keep them.
Welcome to Seasoned Advice by the way, great first question!