You really don't need a keyboard, I use it just fine with onscreen and even wrote some simple scripts in vim with it. Tab completion in the shell helps a lot too and termux's keyboard has a button for it right there.

But if you _do_ need a keyboard... it's android and it perfectly supports USB or Bluetooth input devices including mice, keyboards, etc. If you have a Samsung or some other devices you can even get a nice HDMI output to a monitor and desktop experience out of the box. It's really like a little laptop in your pocket at all times.

And if you need a GUI Termux runs X11, vnc, etc and GUI apps just fine. Just download a X11 server or vnc app from the play store (there are tons) and you're good to go.