I'm really sorry to hear that! I loved Rose of Segunda and the only reason I haven't played my copy of Heaven's Grave yet is because I'm burnt out on VNs and needed a break to play something more traditionally game-y.
Thank you for being open about the situation, down to the finances. I think that kind of openness actually really helps fans realize how much support is needed, rather than pretending everything is a-okay and then suddenly folding with no warning. This is going to be quite a long response, but I hope you find some of it helpful.
General thoughts on Kickstarter: make sure you know what you're getting into when it comes to being able to deliver the rewards you've promised. I've heard lots of stories of people promising posters or something without realizing how much work they'd need to put into organizing, printing and shipping. Also think about the extra expenses you'll be racking up, e.g. money for a good trailer if you aren't making it yourself, the Kickstarter fees.
That said, lots of indie devs rely on Kickstarter to basically pre-sell copies of their games and gauge interest! You wouldn't be alone there, and if you only need a small amount, there's no reason not to ask for it. I'm actually impressed you never Kickstarted any of your previous games.
Kickstarters also double as a way of advertising your games, and I'd say an affordable otome that shows promise, especially if you emphasize that you're an experienced dev that's delivered previous titles without any issues before, could do pretty well.
Ask for more money than you need, because some people are not going to pay up when it's successful. Have both a good trailer and an obvious link to the demo for people to give a whirl. Advertise shamelessly on every possible avenue. Post links to subreddits like /r/otomegames and stay active in the threads. Steal quotes from some of the more effusive reviews to show how much people love your work in the trailer. Whatever it takes.
Kickstarter Rewards: I back Kickstarters regularly. The two reward tiers I go for in games are wallpaper packs, generally ~$5, and digital copies of the game, generally ~$10-15. In your case, BFF has solid art (the best of your games, I think!), but not spectacular, so I probably wouldn't buy the wallpaper tier. (I usually go straight for a digital copy for projects I'm excited about anyway, which I would in this case.)
I'm also more likely to support right away when there's an "early bird" tier for digital copies, where you get a discount if you're within the first X number of people to support that tier.
I know other games usually offer stickers, keychains, posters, etc., but since I don't buy those I'll let others chime in with what they'd want. What I would totally pay extra for is additional backer-only story content of some kind, using the same assets you already have. It would have to be a bonus, rather than gating away main story content, obviously. Maybe epilogues a few years into the future for each route (only if you don't intend to include those as endings already), or bonus scenes that backers get to vote on to choose, e.g. a scene from an AU where the accident never happened. Alternatively, you could use those as stretch goals.
Thoughts on Heaven's Grave: I can think of a handful of reasons why it wouldn't be selling well. One is price—at $17 CAD, you're competing with commercial VNs like WILL: A Wonderful World. That said, I don't want to encourage indie devs to devalue their labour, especially when Heaven's Grave has such a high wordcount.
It might also help to upload the demo to Steam, if you haven't already!