Huge +1 to this plan. Nothing compels one to to learn to swim like being thrown into a shark tank.
For shrinking the overall size of the endeavor, a lot of conferences / meetups have a lightning talk section so rather than filling in 45-60 min of time, you've only got to do about 5 minutes, usually with a hard cut off. It's a great way to get your feet wet.
+1, lightning talks are amazing as a speaking opportunity. They're drastically less scary than a 40 minute talk, so it's easy to give it a go with a simple talk without much prep, and as you gain experience they're an amazing place to practice honing more complex topics down to their essential essence.
I find the social pressure to avoid failing miserably in front of an audience is sufficiently motivating.
Local meetup groups are great, as is giving a talk at your company. If I'm giving a talk, I like to give the same talk to both audiences.