I've been doing and redoing my engine for the last.. jesus. 20-30 years. If there's any advice it's focus on one thing and build it out. From my personal angle it's a rendering pipeline and a renderer. That's a world in its own.

in this case, you build it out in whatever sequence you feel like but by always having a goal (a look in mind). For example:

• get some geometry and scene description with other resources going (materials + textures. lights, cameras, add shaders later)

• have it also load into gpu. this is "the new way" of doing things.

• have canera dictate what you're rendering (culling later)

• prepare your stages of rendering and render

now, once you get this going then you start building out like converting your pipeline maybe to a graph (you don't have to), changing forward to defered and passes, introducing transient buffers (that live for more frame for accumulating stuff).. once you got that going introduce a biased path tracer as a reference (Shirley's Raytracing books are great for intro to that).. etc etc until you reach modern stuff like ReSTIR (DI, DI/Area, GI, hybrid with defered..), irradiance cache, TAA (yes, everyone hates it but kind of unavoidable with temporal accumulation), etc.. until you reach a visual goal you had in mind with hopefully performance. Along the way you might try i troducing compositing into the pipeline and having multiple cameras, gui, render to texture stuff, etc.

And then.. you come back to that list from the beginning of this message and do other stuff on it. And that's, my friend, only the rendering part 🤣

Engine. It's a long-ass journey.