1) The link you show is for MacBooks not MacBook Pros. Do you have a MacBook or a MacBook Pro? If it's a MacBook Model 7,1 then you can use up to 16Gb of RAM. To see which model you have go to the Apple in the upper left corner and select About This Mac, then click on More Info (and then System Report if you’re running 10.7 Lion or 10.8 Mountain Lion). When System Profiler comes up check the Model Identifier and post it back here.
2) More RAM will not affect the Processor.
3) These are good online stores for Mac compatible RAM
OWC http://eshop.macsales.com/shop/memory/Apple_MacBook_MacBook_Pro/Upgrade/DDR3_Whi te - They offer Mac tested RAM at very good prices.
Crucial Memory http://www.crucial.com/ - good place to buy RAM from all over the world. They also have an excellent memory selector that allows you to choose memory based on your computer's model
Data Memory Systems http://www.datamemorysystems.com/apple-memory.asp - another good, cheap place to buying RAM if you live in the U.S.
Here are video instructions on replacing the RAM on the White Unibody.
If you don’t have the tools to open up the MacBook OWC has a set for $5.
Should I uprade the processor or RAM for better results?
The processor cannot be upgraded...That is soldered to the logic board, there is no way of getting it out. The RAM hosever, is replaceable by simply taking the bottom off the MacBook and then pressing the two tabs aside and simply sliding it out and sliding the new back in and locking in place...