COMPILE From Source For Any Phone On Linux Distros [BUILD ENVIRONMENT TO COMPILE]

Hi,

I understand this guide is for compiling from any CyanogenMod and CyanogenMod source-based source for any phone. I have two questions:

1. What steps would need to change (or to be added) if we were compiling from the master branch of the AOSP instead? I can't seem to find a tutorial of how to do it. I am not being able to connect the dots from different sources (being in a bit of an hurry doesn't help it...).
2. I want to build a custom ROM to a device and need to know what I need to ask the vendors for. I understand I might need to create modules and devices for the HAL (and something else? answers to question 1 might help on this) because it is not an officially supported device. What do I need to ask the vendor for and in which format? Do providers usually make drivers available in the format Google does?

I have already spent a lot of time looking for answers here, at the official AOSP page and all over the web, reading and watching videos. There's always something I don't understand. This guide seems to be a very nice starting point. I would be very thankful if someone could help me on this one! I am a software engineer, don't worry about some technical stuff. I just do not have any experience, yet, with embedded systems.

Thanks!