Hi Chanelle, and thank you for the long and thoughtful post.
We definitely want to make finer text editing easier with FlickType, so you can expect features such as moving the cursor by character as well as deleting individual characters to be available soon. We will also work on improving the current automatic spacing logic so that you'll have fewer errors that need correcting to begin with. We are simply starting with the basics, and proceeding slowly but surely with the rest of the expected functionality.
On the issue of the bottom row getting crammed as we add more keys, the most likely option is to simply add back a fourth row and make the keyboard feel almost identical to the iOS one when touch typing, but without affecting the Flick Typing experience at all, ie you wouldn't have to worry about accidentally hitting any control keys. This would also significantly ease new users into the system, where each control key could also offer a hint of how to invoke it using a gesture instead. Easing new users into the system will be a big focus area for us in the near future.
In your email you mentioned, quote: "When dismissing FlickType, finding and tapping the "Send" button is impossible without first double tapping the text edit field in the Messages app". As far as I can tell, you can access the "Send" button when the keyboard is dismissed: it's located at the very bottom right corner. Please let me know if this doesn't work for you for some reason.