Finally, I've made up my mind and ordered a few parts. My robot will look like Stingray but not exatly the same. I am going to use Stingray motors and main wheels. I will make the chassis from black HDPE which is 4 mm thick. The HDPE is a God-send product for hobbyiests. Easy to work with and durable. And, the brain is going to be based on Arduino. In addition to regular ultrasonic sensors, I also plan to use a new cam module which is still alive at this time on Kickstarter. I will put it on a pan tilt servo unit to enable it watch every direction. In a few sentence they describe it as "Pixy is a fast vision sensor you can quickly “teach” to find objects, and it connects directly to Arduino and other controllers." More info can be found at Kickstarter -> Pixi (CMUcam5)
. My initial goals are to have it play in the house, e.g. when I throw a ball I expect him to follow, find and fetch it.
I will post my work as I make progress, because I learned a lot from the other contributers.