1. a cold water extraction will work to remove any water soluable substance from a non-water soluable substance (such as opiates/opioids from apap). think of this in the same way that some substances are soluable in polar solvents, while others are not and are soluable in nonpolar solvents (which is why acid/base extractions work so well; freebase alkaloids are not soluable in polar solvents, but they are in nonpolar, and most of the gunk you're trying to seperate them from are soluable in polar solvents, so you remove the nonpolar layer, then change it back into a salt, and since salts usually arent soluable in nonpolar, the crystals will crash out)
2. you can bang anything you want, but the lower dose pills tend to have more garbage (binders/fillers/wax/etc) in them, which will do mass damage to your veins if constantly shot without careful preperation to remove the gunk. unfortunately i do not know a good, easy way to prepare pharm pills for safe injection, so i cant offer you any help there.
3. you cant snort benzos because they're not water soluable; they just plain cant cross your nasal membraine and enter into your system. i've HEARD that diazapam citrate is water soluable (which would make it both snortable and easy to bang), but i have no real proof of this at this time.