I agree, that if you don't feel that the Kickstarter launch isn't ready, it's better to postpone it.
Some of this might be obvious and may have been mentioned but I'll just add my thoughts in case someone may find it useful.
I should do some research but a lot of what I can find seems to be contradictory.
I've been sorta looking at a few Kickstarter projects over the years to try to learn from their experience in case I ever create one of my own. You're right, unfortunately, there's no magic formula. There are certain aspects that can be considered, but for the most part you only have control over the quality of the Kickstarter presentation material and some aspects of networking/contacting people/press. Ultimately, whether the KS funding succeeds or not is ... a roller coaster ride.
First things first I'm going to focus on things for the trailer, which means finishing off some of the half finished areas (swamps, mountain ascent, temple and castle/tower exterior) and add a few of the one off pieces I wanted to create for the levels that were going to hint at the narrative. Also I need to animate one of the bosses as that'd be a nice way to end the trailer I think.
That's a good start for the trailer. It's good to have at least two very different environments to show that there is variety. Three is probably better but only go beyond that if you have time.
I'd say more important is showing gameplay variety (features, special moves, upgrades or adventure sequences) and, in terms of gameplay, what is unique about your game. Next, it's good to show the character's in-game motivation to give players something to relate to.
Another aspect is that some/many people seem to be interested in the developer in a way of supporting someone trying to realize their dream. Those people seem to like trailers where the developers talks about the project, why they want to create the game and what it means to them. That can create that "extra" connection where supporters will really try to help the developer succeed. Even in recent years where game projects are expected to have at least a decent gameplay footage, I've seen a few projects that had very little in terms of gameplay or content but the developer's enthusiasm seemed to get people excited to join in and contributed to the project being Kickstarted. I'm referring to smaller projects with "unknown" developers and not people with game industry experience. Of course, this might need a certain "presentation personality" to be able to sell that to your audience. At the very least, do describe it in the description.
After the KS launch, communicate frequently.
Reply to comments. I've seen quite a few projects that seemed to ignore people's questions on the comments page.
Updates:
-Certain milestones are met (e.g. 25%, 50%, 75% funding has been reached). Especially if a certain amount is reached faster than expected.
-Mention features (or elaborate on them)
-Show new gifs
-An article/video has been created about the project
-(Other relevant ideas)
If you also use other media (Facebook, etc), it's good to keep people updated everywhere. This might be more important post KS, where I've seen quite a lot of projects focus on one or a few websites but ignored others. For example, for lack of updates on Steam, people often think a project is waporware even though there are plenty of updates on other websites. I know, this is jumping ahead a bit but it's good to plan and decided which websites you want to use for updates. I've seen tumblr used quite a few times. Perhaps people using mostly mobile devices may prefer that over others?
Another aspect is Steam Greenlight. I've seen quite a few projects that posted the game before or around the same time as launching the KS campaign. That can let people know of your game and potentially bring more support and provide some feedback. Especially, as you mentioned if you have a demo that people can try.
In any event, good luck!