I recommend articles by Chad Waterbury and Dan John to start, which you can find on www.t-nation.com (which is a quality resource in general). Dan John tends to recommend simple, effective strategies, and Waterbury writes a lot addressing your first and second questions.

A great place to start, this article by Mark Rippetoe: http://www.t-nation.com/free_online_article/most_recent/most_lifters_are_still_beginners

Eric Cressey and Christian Thibaudeau write great stuff, if you're into a more complicated approach.

Also I agree strongly with Zed's point 2.

I agree with Zed's point 3. about supplements sort of. I think the exceptions are (1) "peri-workout nutrition" about which there are many complex strategies but you can keep it simple, say a whey protein & gatorade shake before or after (or both) your workouts, and (2) things often lacking in a modern diet or lifestyle: fish oil (or some other way to get omega 3) and vitamin D seem to be the most frequent recommendations.