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Textastic 4.0 will have code completion for HTML, CSS and for PHP functions.

Textastic 4.0.2 adds code completion for JavaScript.
Hrmm, it's weird that you don't get crash reports. 

Textastic 4.0.2 is now available on the App Store. I've fixed a few minor issues. Please try it out - maybe if fixes the problem.
Also, it would be nice if you could send me the crash reports. See http://feedback.textasticapp.com/topic/48133-how-do-i-send-crash-reports/
What kind of file are you editing when this happens? 
Implemented in Textastic 4.0.2:

You can press return to accept the top-most entry.
Use the arrow keys on the external keyboard to select a different entry from the list. Hit return to accept the selected entry.
Use the left or right arrow keys to close the list.

For the on-screen keyboard nothing has changed.
Yes, Textastic has syntax highlighting for Java and a huge amount of other languages. Here's a list: http://www.textasticapp.com/v4/manual/lessons/Which_file_types_are_supported.html