I assume you mean with a Bluetooth keyboard? (Not sure the built in has the right keys?)
You should install black mamba, which has some editor shortcuts, which I believe you can customize.
Stash (GitHub.com\ywangd\stash) is something you should also install, as it lets you use a bash-like shell within pythonista. But it doesn't have vim currently.
If you are brave, you could try porting https://github.com/prompt-toolkit to the stash terminal, which would let you use pyvim.