I'm not sure, but does disabling "Indent wrapped lines" in Preferences do what you want?

Never. :)

Textastic is a text editor, not a visual XML editor. You can use an XML formatter/pretty printer like this: http://xmlprettyprint.com and paste the result into Textastic to make the file more readable.

The Mac version currently has no (S)FTP support. That's also the reason why it costs less than the iOS apps. I'll consider adding it in a future version, but I'm focusing on improving the code editor first. On Mac OS X, there are many commercial and free FTP clients that you can use to transfer your files to your servers which is not the case on iOS.

the "true :" in the new line seems to be parsed as a goto label in this case. The same happens in TextMate. If you enter something that is not a valid goto label, it works fine.

Yes, this is a bug in 1.0.

It will be fixed in the next update. 

There's already an option to show tab characters. Spaces are currently not shown.