Which gapps cant be downloaded through the play store/marketplace? I've seen that there are quite many different modular packages of the gapps http://forum.xda-developers.com/showthread.php?t=2397942 and I was wondering if I can install the nano and add the other gapps one by one through the play store. Or if there is by chance some google apps that cant be retrieved with the play store?

Id like to start with a very minimum set of apps if possible (and not to install google now).
Yes, I'm pretty sure all of the other 'Google Apps' can be requested from the Play Store. I myself, also usually start the basis of a new ROM installation with the Nano-gapps package. 

It removes a lot of the non-mandatory Google bloatware such as GoogleNow, PlayMusic (I use an alternative) and even Gmail (I have my Gmail emails come through the stock Email app to avoid duplication).