Hello,

if you are using the full version from the Mac App Store (not the trial version), you should see an iCloud tab in the open dialog (File -> Open) that contains all your iCloud documents. 

Currently not. You can see the complete file name in the text field of the rename dialog: http://www.textasticapp.com/v5/manual/lessons/How_can_I_move__copy_and_rename_files_and_folders.html#step_4

Not at the moment, sorry.

You can add custom syntax definitions to Textastic by using TextMate bundles. See
http://www.textasticapp.com/v5/manual/lessons/How_...

A quick search for "twig tmbundle" in Google brought up this TextMate bundle which should work:
https://github.com/Anomareh/PHP-Twig.tmbundle

You can find a list of hardware keyboard shortcuts at http://www.textasticapp.com/v5/manual/lessons/Whic...

I'm not aware of a shortcut to delete the current line.

I'll see what I can do.

Thanks for letting me know!