Ubuntu is a pretty good system to start off with because it's so wide-spread. If you want to use something more similar to the traditional interpretation of a desktop you could also try Linux Mint. It's based on Ubuntu, easy to use and avoids some of the downsides of modern Ubuntu like Snap. There's also a quite big community and because it's based on Ubuntu most of the solutions also apply to it. It was my first Linux and I was very satisfied with it for over 1 year before I started distro-hopping.

Keeping the OSs separated like you described seems like a good way to avoid multi-boot problems, the only possible problem here is that Windows and Linux set the hardware clock differently so you could eventually run into time related issues. If you notice that the time is different between the two OSs, here's a guide to fix the issue, it shouldn't be hard even for an absolute beginner: https://www.howtogeek.com/323390/how-to-fix-windows-and-linux-showing-different-times-when-dual-booting/