The more plant material you leave on, the longer it will take to dry. Generally, the longer it takes to dry, the better. However, if you just hang the entire plant, you run the risk of growing mold (which will ruin the entire harvest). I think the most common practice is to hang up entire branches after trimming off all the leaves.

Here is a great guide on harvesting/drying/curing. Should answer all your questions. If you have any remaining questions, feel free to ask.

http://boards.cannabis.com/showthread.php?t=53657

And, yes, you can make oil with your trimmings. To make the highest potency oil, only use the trimmings that have trichomes (crystals) on them.

Boiling the roots does nothing. This is just myth.

Good luck!