Hey Norio 😀
in solving the situation that you're describing, something that's great on Mac is 'Mission Control'. its like having 3/4/5, as many desktops as u want, all on one machine 😃
this vid demonstrates it a few years ago, but it has since been updated since then 😃
as far as memory goes, a few years ago 8gb would have been just fine. especially if you're also rocking a SSD. with present apps and software as of 2021 12gb maybe should be something to aim for 😃