It's been a long time, but I believe 2,500 or thereabouts is required by Japan for fluency. As for what the average Japanese person knows, it is easily over 10,000. I think the JLPT requires 2,000 for the highest level of proficiency. A good way to study? Flash cards, of course, and learn the origin of the symbols so that you can break down the more complex kanji into components which might help you understand one you've never seen before. There isn't an easy way to study kanji, just be diligent and keep reviewing until it's second nature.

I'm sorry I can't talk about how much kanji you should know. But there is a famous exam called Kanji-kentei for Japanese people. (http://en.wikipedia.org/wiki/Kanji_kentei) Average grown-up people would think of taking Level 3 or Pre-2 of Kanji-kentei. Level 2 seems suitable for people who are good at kanji. Level Pre-1 and 1 are definitely for buffs. That is just my opinion, though. You can get several examples of each level here(http://www.kanken.or.jp/kanken/outline/degree.html). You can also get some DS games for this exam.

I think that if you know all the 常用漢字, you're pretty good Togo! But I wouldn't even worry about kanji...if you don't know one, just substitute one with the appropriate hiragana or katakana until you do remember it. Good luck!

As far as I have heard from my Japanese friends, they learnt around 1900-2100 Kanjis. So, yeah that's how much you have to know in order to live a life in Japan without the bother or trouble of not being able to read the signs or newspapers etc. (Signs are really important to be able to be read, because even the public toilets have Kanji signs and you don't want to be in trouble pressing the wrong buttons or entering the wrong toilet!) (=^・^=)