Personally I would appreciate pushing ahead the main plot so you have a proper outline of the story you want to narrate, you've got the workings for the map and quest system basically done already so so you could get that much out of the way. I'm not that well-versed on Ren'py though so what do I know. When that's done, you can focus more spaced out updates on the specific characters. Larger content additions but focused solely on one or two people. You can always do this stuff and lock it off until you release relevant character updates.
The main meat of a game like this is the interactions with the romance options, not the overall story, I'm certain you know this, and since it feels to me like you're going, at least on the main plot, for something similar to the original show you can make a rough outline using that and pluck notes here and there for stuff to happen with them. Writing this can't possibly be that hard, you don't have original characters to worry about or Patreon-guided plot threads, you've got set personalities and events you don't have to come up with yourself.
If you go that route you make a popularity poll and go off those numbers to push the individual plots of each character in that order. Sorta like A Town Uncovered is trying to do but you guys don't seem like [REDACTED] so I'm certain you can work something out and be smart about it. Get easy stuff covered first, then when you have a skeleton to plug these things in you can do the harder stuff, like the combat*, puzzles that lead to plot points or finish flag searches, etc. As far as what "enough content" is there's no solid answer, this is a VN so at the very least some sex scenes with each romance option and a resolution at the end of the plot you're going for, interactions between the romance options totally optional. I'm easy to please in that regard.
A good example for a finished product would be something like Insexual Awakening, I don't like to compare games but that game was very good and was paced and structured very well. Fairly short but it had decent mini-games, good art which you guys also have and 6 romance options with a few scenes each + some together, plus 2 extra characters that just gave you scenes for talking to them. (Like that nurse.) Amity Park is a lot more linear than that game though, right now anyway in that one you could do whatever all the time but in Amity Park since it's more story-driven with the chapters being task-based you don't have to worry too much about player choices really except for dialogue.
Just my take. I ramble a lot, and I haven't slept in 2 days so this is probably all completely fucked but I hope it's as legible as some of it was in my head.
*Also as a personal point the combat feels totally unnecessary since it's so barebones and RNG based. You also can't tell when you're meant to win or lose because they all feel or seem the same.
Edit: Holy shit that's a lot of rambling. Oops.