Congrats! Game engines seem like such a gratifying pursuit that flexes every aspect of one’s skills. I just started reading Game Engine Archicture; if I can ever make the time I really want to take a crack at an engine.
It's really a bottomless pit of interesting technical projects. Careful, if your game engine has users other than yourself, it is also a bottomless pit of feature requests and bug reports.
Source: me
Game programming patterns is also an excellent book. I referenced both of these when writing my engine.
This book is really good; I’ve already gotten a lot of ideas from it.
Love that book, great resource for lookup up all kinds of programming topics, whether game related or not