4 GB of RAM is really what you need to run Windows 10 operating system smoothly and of course the more RAM the better and faster your computer will work and run.
But yes you can run Windows 10 on 3 GB of Ram because I have a laptop that has 3 GB of ram and I upgraded it from Windows XP to Windows 10 and it's not the fastest computer but works okay for me browsing the internet and Youtube videos.
But for video processing or other resource intensive things you do on your computer you should have a minimum of 4 GB of Ram and even better 8 GB to 16 GB of ram works much better.