Would this be too much to bite off for my first project?
Except I'd make it avoid thing within the sensors range, not chase them so It can drive around without crashing into things. Im quite good at building it, like the chassis and stuff, but the electronics and programming I'm quite new too.
Suggestions?
If this will be your first attempt at anything with an Arduino then go for it but your kind of jumping in over your head before getting a swim lesson. You may want to play around with some of the example sketches first to try and get a handle on how the programing goes and how to hook basic items up to the arduino. If you had some experience with electronics and coding then sure. But i think you need to take things a little slower to start.
Not a bad choice, but, as digimike suggests, approach it in stages.
Learn how to connect and control the motors that move the robot BEFORE putting them in the chassis.
Learn how to move the servo that holds the sensor, before attaching the sensor or mounting the servo.
Learn how to use the sensor, and what to make of the data you get back, before attaching the sensor to the servo.
Then, learn how to make the robot simply roll forward 5 feet and stop. Then, make it roll forward 5 feet, stop, and back up 5 feet.
Then, forward, turn left, and stop.
Add capabilities one at a time. Get each one working, then put the working code in a function.
You should be able to make the robot go forward until it sees an obstruction with a single function call.
When that function ends, you know that the robot is stopped because there is something in its way.
Then, you can scan to determine if turning left or right is appropriate. Create a scan function that returns -1, 0, or +1 (for clear(er) to the left, straight, or right), and call the appropriate turn function.
Doing this will make it much easier to debug a function (my robot does not turn left correctly) than if you have an 11,000 line loop method.
I too built a robot as my first project and being a newb, made sure as was previously explained to go step by step in making sure I knew how each component worked and was programmer indepently. Unlike you, I had more knowledge on the programming end (though still quite limited) and surprised myself with ingenuity when it came to fabricating a chassis.
Overall making.n obstacle avoidoiding robot is pretty easy and is a great first project IMHO. Plus it's very fun project.
In it's very simplest form just program it to move forward while ping > x and to rotate when that is not the case. You can build in more sophistication from there.
Hi, adding on to what the others suggest I strongly recommend following the tutorials on the arduino website found here : http://www.arduino.cc/en/Tutorial/HomePage
If you follow these step-by-step then you really shouldn't go wrong.
Ok guys thanks alot 
i'll start with the tutorials (as soon as i get my arduino, stupid long shipping times...) And then I'll make a new post when I actually get this started (hopefully about a month)
Thanks again!
As Paul has noted, for any project (especially one that is autonomous!), plan all of your steps, research everything carefully, and take it one step at a time (this also applies to debugging).
This becomes even more true as you build larger creations; imagine just slapping together an top-fuel dragster and expecting it to work - it would most likely just explode (sometimes even with planning and careful prep, it still does).
I am currently working on what will be a larger semi-autonomous/autonomous UGV, based initially on a PowerWheels H2 for the beta vehicular platform; I am taking utmost care to design and program my Arduino, which will initially handle control of drive and steering (plus act as pass-thru for the pan/tilt servos via a servo-driver board); I expect the thing to ultimately weigh close to 200 lbs - there is no way I am just going to build it and hope for the best.
Instead, I am taking things one step at a time, planning everything, thinking about failure modes and what can be done to avert them (ultimately, I am going to add a remote and on-board kill switch; which are backups to software kill switches, communication heartbeat monitoring, etc); I don't want this thing running amok and hurting somebody or destroying property. This planning and such will ultimately help me when I move past the beta platform and on to the actual system (which I am initially planning as a 4WD quadcycle for the platform; much more power, much more speed, much more danger!).
Good luck, and have fun!
Thanks for the info guys but I hope you don't think I'm just going to wing it and hope it works. I understand how much work it takes to build something, I designed and built a medium scale trebuchet that works quite well. As long as my assumption that designing and testing mechanical projects isn't greatly different from electronic ones, (more computer work for the latter) then I should be ok.