if you plan on running traktor or ableton, i’d personally upgrade my ram to its maximum, I had problems running logic until I did this, but I only had 2gb. http://www.ebuyer.com/393027-crucial-8gb-ddr3-1066mt-s-laptop-memory-for-mac-ct2c4g3s1067mceu ebuyer is a good option, and remember the price of RAM ect. rises and falls regularly the link I’ve just posted you I purchased myself, on a good day and got it for just £40, but at one point I did see it for around as little as £30. No reason not to upgrade your ram, however I will say I don’t think macbook pros older than 2009 are upgradeable, I might be wrong. 2010 onwards is what I personally would go for as from a friend of mine who works in computing always told me that they are the most reliable.
Hope this helps 🙂