Hi!
1 Used - Craigslist, flea markets, pawnshops, garage sales,
thrift stores(Salvation Army, etc), ebay, Bikeforums, bike coops.
Will save you money.
2 Craigslist, ebay, Bikeforums, local bike coops.
3 Bikeforums can guide you
4
http://sheldonbrown.com/
http://www.parktool.com/
youtube.com