well as far as the electronics ohms law is one of the bigest things you need to know to get started i don't know of any good sites for that (i went to school for electronics once upon a time so i just dusted off some old books) but here are some cool sites to check out they are mostly parts sites but they have good info and some of them will have the books and info you are wanting.
http://www.turretboards.com/ parts i have done buisness before with this guy and will gladly do more, there is a forum there too
http://www.tedweber.com/ lots of good information and they have kits and some of the best speakers, plus a forum
http://www.guytronix.com/ heres a interesting project
www.sophtamps.ca a little advanced but low voltage less likely to kill yourself
http://www.missionamps.com/ has a good rep
http://www.ceriatone.com/ has a good rep
http://www.diyguitaramp.com/ good info but can be a little hard to follow
http://www.diycustomamps.com/rem_champ.htm this is just neat as **** right here.