I find art to be the most limiting factor at this point. I'm not a great artist (what I can do takes a painstaking long time to finish) and it's hard to satisfy a creative vision with free art assets.
Though i am purposefully using Rust, so even if Godot did it's a bit more awkward. There are Rust libs for Godot, though i'm not entirely sold on the libs quite yet.
My basic thought process is never do anything more than once for the creative work. If i can't find a way to keep overhead obscenely low then long term i will drown in one-offs.
I think the same way with game code. A heavy emphasis on testing, integration testing, etc. I don't have the time to Q&A for all possible regressions, so i have to ensure i do everything i can to make the engine very testable.
Minimizing repeat work is my goal with everything. Also insanely stable builds, i suppose. Ie i don't want a change in an asset to break historic builds or source. My source is tied to the assets at that time. etcetc
edit: And to be clear, i'm not writing a game engine myself. I'm using Bevy atm.
I've been researching solo game dev for decades now, and that definitely mirrors my conclusions so far.
Just keep the end goal in mind and don't reinvent the wheel, unless you desire a career in wheel engineering. While you're working on your stuff, remember that others are also working on their stuff, and a lot of useful things are shared freely and continually popping up new.
Have the courage to recycle your ideas, and the ruthlessness to streamline your development process. Going solo is all about coming to terms with your limitations, and building solutions to work around them. Maximize the impact of work you like doing, while minimizing the necessity of work you don't. Sacrifice your creative vision until only the core remains. Resist the creeping scope of scaling it up, but also keep firm in your artistic requirements. Keep your "must haves" short, solve the hard problems first, manage your expectations, and above all be stubborn enough to tread through it.