1| Although laptop ram that are spec'd for higher frequency's and lower latency's are cheaper and can fit into just about any motherboard ram slot given that you're dealing with a Macbook will require you to use ram that is certified to work with your unit.
2| You may want to
follow through this thread.
3| You could experiment by borrowing ram from your friends and testing them out.
4| The last bit of pondering would have to be the maximum capacity your Macbook can support since the article linked above does state the they officially support upto 4GB of DDR3 ram rated to run at 1.5v.