Recently I decided to try to customize my Windows 10 machine's UI a little bit. My goal was to trim down all unnecessary stuff by Microsoft and make the OS look more classic. The idea wasn't to try to re-create an older Windows interface, but to have it feel retro.
At first, I found Ultimate Windows Tweaker program released in TheWindowsClub blog. It doesn't offer much graphical customization, but I edited some context menu things and the "Pictures", "Music", "Videos" etc. folder visibility in the "This PC" view. The program offers registry editing using it's GUI.
Next, I installed ClassicShell, but quickly changed to OpenShell because it's still maintained. With OpenShell I could tweak the start menu contents and look. I managed to sculpt the start menu items to my liking, but I still needed some classic Windows icons.
I found Alex Meub's Windows 98 Icon Viewer app with the accompanying blog post about the icons.
Some icons I used as-is, some I edited to my liking. To avoid the retro icons clashing with more modern icons, I created custom icons for some of the programs I have on my desktop.
To quickly create .ico files from my PNG images I used www.icoconverter.com.
For the start menu button I used redblade8's re-creation of Windows 95/98 start menu button. I edited it a little bit to suit my needs.
The tricky thing with OpenShell is that the custom start menu button graphic has to split in 3 sections. The parts represent normal, hover, and active button state, from top to bottom. In this case both the normal and hover graphics are identical, so there is no hover effect.
As for the taskbar, that I didn't bother to try to tweak. So far I've kept it as the Windows 10 default.