I would advise to upgrade to 8GB since you won't be able to do it later (RAM soldered).
The SSD can be upgraded later so you could stick to the default option on that front and save money.
In terms of the CPU, it depends on your usage. I don't think you will notice a big difference unless you are an intensive user of the CPU (most people aren't).
So if you stick to the stock options and only upgrade the RAM to 8GB, you should be good to go.