You can have an all-consuming crush on a person and flirt with them constantly, but that person might only pick up on a few tiny messages and simply think you're being nice. With that in mind, I think you should be more playfully flirtatious and bold. You missed a big opportunity to do this when she was joking about being an undateable toad. This is where you, in your own witty style, let her know that you'd like to go out on a date with her. Make it fun and make it light.
Nothing cramps a first date like the weight of the future.
You learn so much about a person after only one date. It's usually clear that either some spark is there or it isn't. I'd like to get all of you to the point where this first date isn't so daunting. It's really just an extension of your first meeting. At some point after several dates, a relationship begins.