So far, there isn't exactly a "best answer" for each choice. Every answer they like will give raise their affection the same amount.
I will definitely change the tutorial to make it way more clear how the system works, I see a lot of people are confused and have questions. Not 100% sure if I'm willing to add a hint system, because I want to stick to realism as much as possible. Give answers you would give in real life and don't stres about giving the right answers.
Kaedama is not going to lock you out a route just because you said something a character didn't like.
As for a harem ending. Unfortunately, there is not going to be an ending where you end up dating all 17 girls. However, if you play it smart, you could date multiple girls at once, just not the ones that are friends with each other, because they are going to talk amongst themselves.
I'll just leave this tip for others that are scratching their head as well. Affection only increases/decreases with the characters that are present, so characters that don't hear you give an answer, won't know what you said, so it's not going to affect them in any way.
Approach it as you would approach a real conversation and if there are any inputs that aren't working, by all means, message me, so I can fix it.