I have a D90 whicj I have used to photograph people pets and some weddings. Have used all the settings. I'm sure the D300s can be customized more and is faster in continuos mode and with 51 point autophocus has serious advantages...but, I think if you took the same picture with the D90 and the D300s in auto...not even sure if D300s has an Auto mode...I don't think you would notice any difference at all. Outgrow the D90 first before upgrading. Buy better 'glass' for the D90 for the difference in price. Then you can also use the better lenses if and when you get the D300s or even a later better model. I took simultaneous pictures at a wedding with a professional photographer using a D300 and when I compared the pictures at least on the computer screen, I could see no difference. When I printed out the ones from D90, all people had to say was "wow'!
Shooting in the outdoors and sports is exactly what the D300s is built for. It is well sealed from the elements and built like a tank. Additionally, regarding sports, it has a very good frame rate...you won't be disappointed.
As best as I can tell from the Amazon listing, you have the choice of buying the body only, or the body and one lens. I think I actually bought my Nikon D300S at B&H Photo (out of NYC, but they have an online store), and it came with a standard 50-150mm Lens, the charger and battery, and the papers. I am not sure about this one for sale on Amazon. I am reasonably sure that it is truly a Nikon, however. I have probably had my camera now for five years, and it has been a good, reliable one. I have had no trouble with it. Good luck, whatever you decide, and I hope I was some help to you.
You have to ask the seller. Click on the actual camera you are interested in and then the sellers name should be clickable. Ask them what the "shutter actuation count" is if they know it. This area is just for basic questions about the camera model. Good luck!