How to know how much CPU and RAM I need for new computer? I got a pimped up macbook pro (i7 3.3GHz i7) from late 2016 atm, but I feel like I could use a less powerful machine.

I would like to find out what's my current/peak average CPU and RAM usage to see if the new MBA has what I need for what I do. I'm hopeful there is a better way than to constantly look at activity monitor, and manually logging, to get this kind of info. 

I'm not afraid to go into the terminal
You could get a 3rd party app like System Pal or iStat. Both apps reside in the menu bar and tell you things like memory used and CPU usage. You can easily monitor either of these apps. I prefer System Pal to monitor memory and CPU usage. It just gives the top processes.

Another option is to use "top" or "htop" from the command line. These processes are like Activity monitor except it runs via the command line.