what to buy: effects or a 5 string?

I would get the bass first and try it,you might be happy with the strings that it comes with, if not then buy some different strings. But when changing string guage it is quite often necessary to adjust the strig height and intonation - so I suggest that you keep a bit of spare cash for a string change and setup at your local guitar shop/techie. As I found out recently with an online guitar purchase - they dont always come set up properly. But saying that other basses I have purchased online have been fine.

That measurement refers to the overall width of the nut and doesnt really help with identifying the string guage.

I have tried out the bass in a store and the strings were really loose, which is why I wanted to change them. I'm buying it online to get the color that I want