I wish I could work on it full-time. However, after reading a lot about indie game developers, and judging from my situation, it seems like keeping it as a side project is a better decision for me from a financial and mental health standpoint.

Keep up the good work on Metropolis 1998! I have followed your work and the dev community you built around it and it is very inspiring.

Correct, though alternatively indie can resort to kickstarter (factorio) or patreon. Then do early access on steam.

However yes the pressure is different than full time job

TIL Factorio was funded on Indiegogo!

But yes, I'm really not ready for that kind of pressure and marketing efforts. I feel - and even more so since Cities:Skylines 2 announcement - that there isn't enough I can do alone to turn this into a full-time job.

You should definitely at least get a Steam page up so that we can wishlist it. Today's HN posting would have gotten at least one wishlist (from me :) When a game gets enough wishlists on Steam, the game is promoted to various lists which get shown constantly to people (as soon as you have game released and purchasable, even if Early Access). You are otherwise penalized if you create a store page late and have very few wishlists, since Steam's algorithms prioritize giving the banner spots, etc. based on your # of wishlists.

Source: https://www.youtube.com/watch?v=E656RcGWcEs

Is Metropolis 1998 going to be Windows-only?

In the short term, yes. But the game is using SFML and C++, so most ports are possible.