OP:
A warning:
If the 2008 MBPro still has a spinning hard drive in it, you may be very disappointed in its performance after you upgrade to El Capitan.
I realize that the concept of "performance" is a personal judgement, but the most recent versions of the OS seem to have been cooked up on Macs with SSDs, and this reflects the speed of the OS on older systems.
I'm not saying that El Capitan won't run on an '08 MacBook -- however, the overall experience may feel more like "walking" than "running".
For an '08, I'd put Mountain Lion 10.8.5 on it, and then "let it be"...