Possibility of moving on Nexus 5 (AOSP android 6.0.1 M4B30Z)

[gongzelong0718]

Prerequisite：
I used my computer to build the native AOSP android 6.0.1 M4B30Z and flashed it to my Nexus 5.

The first thing I am worried about is that the codes will be very huge as I only have totally 256G storage and only 70G available.What is the expected computer storage?

Secondly, I notice that in the readme https://github.com/SmartisanTech/android, it seems that it can work on Nexus 6 based on Smartisan master base code.
Is it possible to merge the codes to the codes (AOSP android 6.0.1 M4B30Z) and build successfully on Nexus 5?

Last but not the least,I notice that there are several repos on github. If I want to implement the big bang feature, what codes should I need to download? By the way, why are the codes in one repo?

Appreciated it if there is any reply.