I didn’t know some of these things on Linux until today. Shame on me. I’m going to summarize it here.
How to get number of CPUs?
$ lscpu
$ cat /proc/cpuinfo
How many disks on a system?
$ sudo fdisk -l
$ lsblk -S
$ lsblk -d
Free memory?
$ free -h
Free Diskspace?
$ df -h