You can always replace art assets. Look at a game like Magical Camp - it started with default assets but as it gained popularity people started contributing art and the dev had more funds to work with when it came to commissioning custom stuff.
Start simple with a good premise and satisfying gameplay loop and add complexity that builds on these; don't try to get a hundred complex mechanisms working before you've even got the basics in place.
That's generally true, but also varies based on the game. (For example, not fleshing out a gameplay loop might force you to revisits dozens or hundreds of maps later on and comb through the events to update variable & switch checks & placements based on your changes to the way you handle say, a sexual desire system that tracks your likes & dislikes and opens or locks options based on that, or a character's development in sexual skills as they grow more experienced.)
You can only use basic assets if basic assets already exists, and you are allowed to use them in a commercial game. (patreon counts as commerical)
If we use tall sprites, and we want to populate a map with NPCs, those have to be drawn first, because no default exists.
The same is true for enemy sprites - or busts. If you want the player to be able to fight enemies, those enemies have to be visually represented. (And you can't simply snatch art from google for that.) If you want to have dialogues where important characters (main characters, story-characters, quest NPCs) can react visually, you need the bust and you need the expressions.
Since Incandescent Shade emphasizes story and combat, we don't have a small-scale situation where we can put the player on 1 hub map, 3 dungeons, and have them go at it. For the overall game, that's positive, because there's no "forcing players to grind to keep them busy" but it also means that if we want players to have interesting quests, those quests do need people they can visit on the map (character sprite), talk to in dialogue (bust + expression) and at times defeat in combat (enemy artwork).
For a single character or enemy, that can consume an entire week or more.
And that, unfortunately, means that we'll have to already meet quite the standard before we can even hope to try to build a supportive community like that with the first build.
Ultimately, in retrospective, we should have decided to develop an entirely different game that exists on a much smaller scale and isn't nearly as ambitious, at least for our first game. But...that wouldn't have been the game that we want to develop.
Sometimes there are no good solutions. All you can do is keep moving forward, hoping you'll reach the point at which things develop their own momentum.