System Data

Linux stores a lot of system data in files within the /proc directory. Most of the data that this project requires exists in those files.

Operating System

Information about the operating system exists outside of the /proc directory, in the /etc/os-release file.

There are several strings from which to choose here, but the most obvious is the value specified by "PRETTY_NAME".

Kernel

Information about the kernel exists /proc/version file.

Memory Utilization

Information about memory utilization exists in the /proc/meminfo file.

There are a variety of ways to use this data to calculate memory utilization.

Hisham H. Muhammad, the author of htop, wrote a Stack Overflow answer about how htop calculates memory utilization from the data in /proc/meminfo.

Use the formula that makes the most sense to you!

Total Processes

Information about the total number of processes on the system exists in the /proc/meminfo file.

Running Processes

Information about the number of processes on the system that are currently running exists in the /proc/meminfo file. 

Up Time

Information about system up time exists in the /proc/uptime file.

This file contains two numbers (values in seconds): the uptime of the system (including time spent in suspend) and the amount of time spent in the idle process.

From the man page for proc