Today's version of icewm takes around 16mb of memory, xorg will add a bit to it.
There are smaller window managers but I choose this one as an example as it gives a similar experience to the windows xp of olds.
I have done the experience on slimming as much as possible a desktop. But once you start a web browser with more than 3 tabs memory usage goes through the roof. In the end if you want to run an old system with 512mb of ram you are kind of forced to use the web sans javascript and images. You are almost better off using links or w3m and tui apps for everything. Netsurf can work too if you are limiting the number of tabs open.
One a 1GB system you can definitely use a modern web browser but you definitely need the ad/trackers removal extensions and have to take good care of not opening more than 2-3 tabs or you will start swapping a lot.
