Lots of Linux distributions are specifically built for older laptops! And all of them tend to run pretty well on lower end equipment. Here's a list that also mentions the specs needed for each one: https://linuxsimply.com/best-linux-distros-for-old-laptops/
Linux Mint, probably the most popular one on all computers nowadays regardless of specs, has a minimum RAM requirement of 2GB with 4GB recommended :) they make Linux distros for old tiny Raspberry Pi computers so even if your computer is a hundred years old you'll probably be able to run TinyCore on it at least
Yeah!! I haven't had any trouble with it yet, my laptop has only one SSD slot which is why I did it on the same one. I just switch when I boot up. I have the Windows one just in case I can't get a game to run and to access my work's shared drive (absolutely cannot figure it out on Linux lol)