i'm looking to make some shelves..
2 in thick shelves is a bit much dont you think? it could be done but not sure your're going to be impressed with the condition of the wood underneath...give it a try and see...
it's possible, but not adviseable as the timber is normally well worn and contaminated which may result in damage to your tools -especially if you using electric sanders etc. if you are certain that you can clean the timber of all nails etc then go for it but oil those elbows as you will need plenty of polish
If these are going to be junk shelves in your garage then by all means go for it, but they will not turn out great for something like nice shelves in your house. You would be better off getting some nice cheap pine for that.
I have built two picnic tables out of this type of boards. I checked them for nails and other metel with a metel detector, then I ran them through my planer taking approx 1/16th off of each side. I finished with a water treatment. tables look great and are very heavy duty. the boards are generally made of oak. should look good