Ive read that out of 14 pins 6 provide PWM
On a 328-based Arduino, this is true. On the Mega, there are more PWM pins. The Teensy 3.0, developed and marketed by a regular here also has 10 PWM pins, and can be programmed using the Arduino IDE.
so can I use one of those 6 PWM pins for controlling R or G or B?
Yes. If you want each stripe to be a different color, though, you need 9 PWM pins.
Buying the wrong one just means that you'll end up with two. That's not a bad thing. I have 8 spares right now. That makes it easy to test a small sketch and hardware on one, without interfering with the big sketch (and hardware) being developed for another one.