Newb YZ450F Maintenance

I just purchased my first mx bike yesterday because my bestfriend has been wanting me to get one. I fell in love with the sport a little earlier this year, however, I don't know CRAP about the mechanics of the bikes and whatnot (YET). Now that I have my own mx bike, I want to be sure that it's well maintenace and I also need to refurbish it a tad-bit.

I bought a used '07 Yamaha YZ450F from a dealership. It was pretty banged up from the previous owner - mainly cosmestic, but it still had some major damage especially with the exhaust pipe.

So here are my questions:
1. As for a replacement exhaust, any recommendations? I've been riding on an actual mx track -- I don't actually race or anything, however I want something to push me close to that.

2. What kind of maintenance should I undergo with a bike like this? Unfortunately I didn't receive an owner's manual therefore I don't have any real maintenance info on it. It's a 4-stroke bike -- and I'm saying for overall general maintenance for the duration that I own the bike.  

ok read this will tell you all you need to know ok hope i helped!!!!!!!!! as far as exhaust how much are you willing to spend lol get back to me thanks!!!!!

http://www.dirtrider.com/tech/141_0809_dirt_bike_maintenance/index.html

you know how to copy this site right???  
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Autismspeaks.org   check it out
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life in the fast rut!!!!
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my rides- 2008 yz250f fully modified, use to be j-laws bike
        &
IT400 1979 yamaha!!!
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Home: SO CAL

On top of the link yz250f4ever gave you, your first step to learning the proper maintenance is to get the service manual. Wether you got one with the bike or not, get one first thing and read it.
Being new this will help you more then anything else and you wont have to guess at if you ask all the questions you should have.

We will still help you with what ever you need but try this first.  
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I love this dirt stuff.