Hi Dan,
Thanks for your review!
I'm still ironing the bugs (esp. with the soft keyboard), when it's ready I'll create a "booklet" too.
Some general recommendations for Textadept 
This is an "advanced" text editor, with complex features. It is best for those who need to write a lot - and be productive. So it's a joy to use with an external keyboard, but quite painful to use with a screen keyboard. And, as it depends a lot on modifier keys like Ctrl and Alt, currently it's mostly unusable with the Kindle soft keyboard, that lacks these keys.
And, unfortunately, connecting external bluetooth keyboard is a very advanced procedure, not recommended for non-developers (and even that is not guaranteed to work)
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If you still wish to try it without external keyboard, I recommend using the terminal version! It has all the features of the GTK version (kudos to the original dev!) and the software keyboard is complete and reliable.
The terminal version is recommended even with BT keyboard. The GTK interface is much slower and struggles to keep updating if you type even at a medium speed.
One shortcut to keep in mind: Ctrl-Shift-P (kterm)/Ctrl-P (GTK) brings up the command palette where you can quickly access any command, just type a few letters.
If you want to go deeper, read the included documentation (especially the Editing chapter from manual.html and the keyboard shortcuts in api.html). It will unleash the full power of this little editor!
P.S. To close Textadept from command line, type Ctrl-Q. To close the graphical version, click the File menu, then select Quit. No need to restart the Kindle.