IMO "sell flower" interaction should be replaced with "seduce" or something similar if you don't have any flower since it doesn't make sense to sell one when you have none
you gotta get shrine maiden ring from Hilda at maiden village, talk to her and call her mother in the dialog, well you can just read the walkthrough guide at first post for more detail.
I already figured out how to get in, and I've unlocked everything. Regarding the endings, they say there are 21, that's what I saw in a comment. I've only found 5. It's a good game; it entertained me for several days. If someone figures out how to get all the endings, I might play it again to get it 100%.
IMO "sell flower" interaction should be replaced with "seduce" or something similar if you don't have any flower since it doesn't make sense to sell one when you have none
You don't miss much as far as I remember, although if you feel curious regardless, you can save beforehand, give it a look, and then go on with your playthrough