I also usually play without bitters, so there’s no time pressure
This is what I did when I started as well. Factorio, in my mind, is a logistics/building game, not a combat game. Playing without biters lets you learn the base building techniques.
As for not getting overwhelmed with the base, make sure to divide and conquer. Break up the next goal into smaller projects, and work on those one at a time.
Also, leave space between your assemblers. You can always build out more.
I am waiting for Apollo to die, which according to Christian, will be June 30th.