Well, it is definitely not a suicide mission. At least in my Sciter I've implemented all those by myself in reasonable time frame - first version was made in 9

Well, it is definitely not a suicide mission. At least in my Sciter I've implemented all those by myself in reasonable time frame - first version was made in 9 months. But "yes", you need some prior experience, in order to come up with flexible architecture that will allow to expand it further without major redesigns. First version had DOM/CSS and used just GDI. GPU support (Direct2D, OpenGL|Metal|Vulkan via Skia) was added later with API staying the same.